Iterate the Map and temporarily store the key nodes to be deleted then
delete the nodes from the key list ?
Le 28/12/2023 à 14:53, DrPi a écrit :
Iterate the Map and temporarily store the key nodes to be deleted then
delete the nodes from the key list ?
Not clear. Rephrasing it.
Using 2 steps by iterating the Map and temporarily store the keys of
nodes to be deleted then delete the Map nodes using the key list ?
On 2023-12-28 14:59, DrPi wrote:
Le 28/12/2023 à 14:53, DrPi a écrit :
Iterate the Map and temporarily store the key nodes to be deleted
then delete the nodes from the key list ?
Not clear. Rephrasing it.
Using 2 steps by iterating the Map and temporarily store the keys of
nodes to be deleted then delete the Map nodes using the key list ?
[Disclaimer. I am not talking about the standard library]
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
2. It is safe to walk whatever set of map keys, deleting items of the map.
In both cases #1 positions, #2 keys are invariant to the operation of deletion.
Le 28/12/2023 14:53, DrPi a crit :
Iterate the Map and temporarily store the key nodes to be deleted then
delete the nodes from the key list ?
Not clear. Rephrasing it.
Using 2 steps by iterating the Map and temporarily store the keys of nodes
to be deleted then delete the Map nodes using the key list ?
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:umk6ds$e9hc$1@dont-email.me...
...
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
A sane implementation of a map does not have/require an ordering of keys.
So
the idea of "reverse" or "forward" does not make sense for a general map. (There are, of course, special cases where the keys have an order that matters to the map; the standard ordered map is like that.) Assuming an ordering is exposing the implementation unnecessarily.
You always complain about mixing implementation with interface, but you are clearly doing that here. That technique really only works if the data structure is implemented with an underlying array. If you have separately allocated nodes, deletion might completely destroy a node that the iterator is holding onto. Avoiding that takes significant efforts that sap
performance when you don't intend to modify the container you're iterating (which is the usual case).
My longstanding objection to the entire concept of arrays is that they are not a data structure, but rather a building block for making data
structures.
One wants indexed sequences sometimes, cheap maps othertimes,
but arrays have all of the operations needed for both, along with other capabilities not really related to data structures at all.
It's way better
to declare what you need and get no more (visibly, at least). That makes it way easier to swap implementations if that becomes necessary - you're not stuck with a large array that really should be managed piecemeal.
"DrPi" <314@drpi.fr> wrote in message
news:umjuvc$9sp$2@rasp.pasdenom.info...
Le 28/12/2023 à 14:53, DrPi a écrit :
Iterate the Map and temporarily store the key nodes to be deleted then
delete the nodes from the key list ?
Not clear. Rephrasing it.
Using 2 steps by iterating the Map and temporarily store the keys of nodes >> to be deleted then delete the Map nodes using the key list ?
If the keys are messy to save (as say with type String), it might be easier to save the cursor(s) of the nodes to delete. You would probably want to use a cursor iterator (that is, "in") to get the cursors. Code would be
something like (declarations of the Map and List not shown, nor is the function Need_to_Delete which is obviously application specific, Save_List
is a list of cursors for My_Map, everything else is standard, not checked
for syntax errors):
Save_List.Empty; -- Clear list of saved cursors.
-- Find the nodes of My_Map that we don't need.
for C in My_Map.Iterate loop
if Need_to_Delete (My_Map.Element(C)) then
Save_List.Append (C);
-- else no need to do anything.
end if;
end loop;
-- Delete the cursors of the nodes we don't want anymore.
for C of Save_List loop
My_Map.Delete(C);
end loop;
Randy.
On 2023-12-29 04:20, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:umk6ds$e9hc$1@dont-email.me...
...
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
A sane implementation of a map does not have/require an ordering of keys.
Yes, but iterating a map requires ordering regardless properties of the keys.
On 29.12.23 10:51, Dmitry A. Kazakov wrote:
On 2023-12-29 04:20, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:umk6ds$e9hc$1@dont-email.me...
...
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
A sane implementation of a map does not have/require an ordering of
keys.
Yes, but iterating a map requires ordering regardless properties of
the keys.
Suppose that there is a way of orderly proceeding from one item to the
next.
It is probably known to the implementation of map. Do single steps
guarantee transitivity, though, so that an algorithm can assume the
order to be invariable?
At the start of the algorithm, the assumption of order of items implies
an ordered sequence of all the keys.
Someone might want to use this known
order for a cache of "index values". It might be the implementation
that does so.
Insane? Or just tampering? (Randy Brukardt's example demonstrates
the mitigation using Cursor, I think.)
Maybe the bulk operations of some DBMS' programming
interfaces work just like this, for practical reasons.
Ada 202x' Ordered_Maps might want to add a feature ;-)
procedure Delete (Container : in out Map;
From : in out Cursor;
To : in out Cursor);
That's what I did but I saved the keys (String) instead of the cursors.
Does it make a difference ? Performance maybe ?
On 2023-12-29 04:20, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:umk6ds$e9hc$1@dont-email.me...
...
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
A sane implementation of a map does not have/require an ordering of keys.
Yes, but iterating a map requires ordering regardless properties of the
keys.
So
the idea of "reverse" or "forward" does not make sense for a general map.
(There are, of course, special cases where the keys have an order that
matters to the map; the standard ordered map is like that.) Assuming an
ordering is exposing the implementation unnecessarily.
It always does sense *IF* enumeration (needed for iteration) is provided. Enumeration of pairs (<key>, <value>) is not same as ordering values by
the keys.
No. First, it is two different interfaces. A view of a map as:
1. An ordered set of pairs (<key>, <value>)
2. A mapping <key> -> <value>
Second, the point is that both are array interfaces. The first has
position as the index, the second has the key as the index.
Both are invariant to removal a pair and any *sane* implementation must be
OK with that.
The problem is not whether you allocate pairs individually or not. The insanity begins with things unrelated to the map:
1. OOP iterator object.
2. FP iteration function.
Both are bad ideas imposed by poor programming paradigms on implementation
of a clear mathematical concept. That comes with constraints, assumptions
and limitation array interface do not have.
for Index in reverse Map'Range loop
Map.Delete (Index);
end loop;
would always work.
Arrays have interface and implementation. The array interface is a mapping key -> value, the most fundamental thing in programming.
An array implementation as a contiguous block of values indexed by a
linear function is a basic data structure that supports the interface.
Sure. The problem with Ada is that it does not separate array interface
from its built-in array implementation and does not separate record
interface and implementation either.
Now, tell me that you have a longstanding objection to the entire concept
of records... (:-))
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:umm4r5$ppag$1@dont-email.me...
On 2023-12-29 04:20, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in messageYes, but iterating a map requires ordering regardless properties of the
news:umk6ds$e9hc$1@dont-email.me...
...
Provided a sane implementation of map.
1. It is safe to loop over the map items in the *reverse* order of,
deleting whatever items.
A sane implementation of a map does not have/require an ordering of keys. >>
keys.
Only as far as there is an order implied by the order that things are returned. That order doesn't have any meaning, and certainly there isn't any such thing as "forward" or "reverse" to it. (Which was the original claim, after all.) There is no "natural" order to the key/element pairs; they are effectively unordered.
It always does sense *IF* enumeration (needed for iteration) is provided.
Enumeration of pairs (<key>, <value>) is not same as ordering values by
the keys.
True, but it doesn't imply any particular ordering. Certainly, no concept of "forward" or "reverse" applies to such an ordering (nor any stability requirement).
Practically, you'll get the same order each time if the
container isn't modified, but if it is, all bets are off. (If the container is changed by element addition or deletion, the index may get rebuilt [hash table reconstructed if too full, tree-index rebalanced, etc.] and that can change the iteration order dramatically.)
No. First, it is two different interfaces. A view of a map as:
1. An ordered set of pairs (<key>, <value>)
This is not a map (in general). There is an *unordered* set of pairs. You
can retrieve them all, but the order that is done is meaningless and is an artifact of the implementation. There's a reason that maps don't have
reverse iterators.
2. A mapping <key> -> <value>
Second, the point is that both are array interfaces. The first has
position as the index, the second has the key as the index.
"Position" is not a property of an (abstract) map. That's my complaint about looking at everything as an array -- one starts thinking in terms of properties that things don't have (or need).
Both are invariant to removal a pair and any *sane* implementation must be >> OK with that.
The only sort of position that you could possibility talk about for a map is the ordinal order that an iterator returns key/element pairs.
But that
necessarily changes when you insert/delete a pair, as that pair will occur
at some (unspecified) point in the ordinal order. Otherwise, you won't have the performance expected for key lookup in a map.
The problem is not whether you allocate pairs individually or not. The
insanity begins with things unrelated to the map:
1. OOP iterator object.
2. FP iteration function.
Both are bad ideas imposed by poor programming paradigms on implementation >> of a clear mathematical concept. That comes with constraints, assumptions
and limitation array interface do not have.
??? Abstractions are "poor ideas"?
You have some problem with an iterator
interface as opposed to an array interface??
for Index in reverse Map'Range loop
Map.Delete (Index);
end loop;
would always work.
It only works if you think of Map'Range as an iterator object. Otherwise,
you would have to impose an extra "position" interface on the map (or other container), and at a substantial additional cost in time/space. Containers
in general don't have "positions", elements are unordered unless the container imposes one.
Arrays have interface and implementation. The array interface is a mapping >> key -> value, the most fundamental thing in programming.
That's only part of it. It also includes the idea of "position",
including calculated positions,
the operations of concatenation and slicing,
and (for
Ada at least) ordering operations. If the array interface was *only* a mapping I would not object to it. Maps do not have a natural order, and nothing should be depending on such order. There is no meaning to the third pair in a map.
An array implementation as a contiguous block of values indexed by a
linear function is a basic data structure that supports the interface.
Right: the much more complex interface I note above. And that's the problem. You don't even seem to realize all of the unnecessary baggage that arrays carry with them.
The problem with arrays is that the mapping part is tied to many other supposedly fundamental capabilities that aren't fundamental at all.
Even
intellegent people such as yourself have been using arrays so long and so primitively that you've gotten blinded to the fact that basic data
structures really have only a handful of operations, and the majority of the "fundamental" capabilities aren't needed much of the time and certainly should only be provided when needed.
"DrPi" <314@drpi.fr> wrote in message
news:ummj1i$e64$1@rasp.pasdenom.info...
... (Example eliminated)
That's what I did but I saved the keys (String) instead of the cursors.
Does it make a difference ? Performance maybe ?
It certainly will make a performance difference; whether that difference is significant of course depends on the implementation. There's two parts to it (one of which I thought of yesterday and the other which I forgot):
(1) The cost of storing keys vs. storing cursors. Cursors are going to be implemented as small record types (cannonically, they are two pointers, one to the enclosing container and one to the specific node/element). A key can be most anything, and storing that can be more costly.
(2) The cost of looking up a key. A map is a set of nodes, and there needs to be some operation to associate a key with the correct node. Those operations take some time, of course: for a hashed map, the key has to be hashed and then some sort of lookup performed. Whereas a cursor generally contains an indication of the node, so the access is more direct.
For a lot of applications, this difference won't matter enough to be significant. But I'd probably lean toward using cursors for this sort of job as that would minimize performance problems down the line. (Of course, if
the container gets modified after you save the cursors, then they could become dangling, which is a problem of it's own. If that's a possibility, saving the keys is better.)
Suppose that there is a way of orderly proceeding from one item to the next. >> It is probably known to the implementation of map. Do single steps
guarantee transitivity, though, so that an algorithm can assume the
order to be invariable?
An insane implementation can expose random orders each time.
Unless removing element invalidates all cursors. Look, insanity has no bounds. Cursors AKA pointers are as volatile as positions in certain implementations. Consider a garbage collector running after removing a pair and shuffling remaining pairs inmemory.
Maybe the bulk operations of some DBMS' programming
interfaces work just like this, for practical reasons.
Ada 202x' Ordered_Maps might want to add a feature ;-)
procedure Delete (Container : in out Map;
From : in out Cursor;
To : in out Cursor);
Here you assume that cursors are ordered and the order is preserved from call to call. Even if From and To are stable the range From..To can include random pairs in between.
On 29.12.23 17:52, Dmitry A. Kazakov wrote:
Suppose that there is a way of orderly proceeding from one item to
the next.
It is probably known to the implementation of map. Do single steps
guarantee transitivity, though, so that an algorithm can assume the
order to be invariable?
An insane implementation can expose random orders each time.
An implementation order should then not be exposed, right?
What portable benefits would there be when another interface
is added to that of map, i.e., to Ada containers for general use?
Would it not be possible to get these benefits using a different
approach? I think the use case is clearly stated:
First, find Cursors in map =: C*.
Right after that, Delete from map all nodes referred to by C*.
For deleting, this thread has shown a loop that calls Delete
multiple times right after collecting the cursors.
And it is boilerplate text. Could Maps be improved for this use case?
[Bulk deletion] We do get bulk insertion in containers. Also,
A.18.2 already has bulk Delete operations. Similarly,
the Strings packages have them.
[No thread safety needed] If standard Ada maps are usually operated
by just one task, stability of Cursors is predictable.
Then, with or without automatic management of storage,
when My_Map is from an instance of Ordered_Map,
Start := In_13th_Floor (My_Map.Ceiling (13.0));
Finish := In_13th_Floor (My_Map.Floor (Fxd'Pred (14.0)));
My_Map.Delete (
From => Start,
Through => Finish);
second container, you would return the square one! (:-))Would it not be possible to get these benefits using a different
approach? I think the use case is clearly stated:
First, find Cursors in map =: C*.
Right after that, Delete from map all nodes referred to by C*.
Right. Find cursors, store cursors in another container, iterate that container deleting elements of the first. Now, consider that the cursors in the second container become invalid (dangling pointers). If you wanted to delete them immediately from the
On 01.01.24 21:55, Dmitry A. Kazakov wrote:
Would it not be possible to get these benefits using a different
approach? I think the use case is clearly stated:
First, find Cursors in map =: C*.
Right after that, Delete from map all nodes referred to by C*.
Right. Find cursors, store cursors in another container, iterate that
container deleting elements of the first. Now, consider that the
cursors in the second container become invalid (dangling pointers). If
you wanted to delete them immediately from the second container, you
would return the square one! (:-))
OK, yet if indicating nodes in a container is designed to survive
any deletions, leaving nothing dangling i.e., doesn't this limit
the way in which implementations can store nodes?
Seems like every "pointer" (= (Container, Position)) needs to know
its element, and/or the container will have to equip its storage
management with a "vacuuming" algorithm accordingly.
Transactions seem more flexible (a locking flag in a sequential
algorithm?), a dedicated operation looks simpler than both.
Only as far as there is an order implied by the order that things are
returned. That order doesn't have any meaning, and certainly there isn't
any
such thing as "forward" or "reverse" to it. (Which was the original
claim,
after all.) There is no "natural" order to the key/element pairs; they
are
effectively unordered.
Iteration = order. It is the same thing. If you provide iteration of pairs
in the mapping by doing so you provide an order of.
It always does sense *IF* enumeration (needed for iteration) is
provided.
Enumeration of pairs (<key>, <value>) is not same as ordering values by
the keys.
True, but it doesn't imply any particular ordering. Certainly, no concept
of
"forward" or "reverse" applies to such an ordering (nor any stability
requirement).
It does. You have a strict total order of pairs which guarantees existence
of previous and next pairs according to.
True, an operation may invalidate whatever invariants. It applies equally
to any orders, any cursors and pointers, any hidden states of pending
foreach operations. Sanity means which invariants the implementation
keeps.
"Position" is not a property of an (abstract) map. That's my complaint
about
looking at everything as an array -- one starts thinking in terms of
properties that things don't have (or need).
Yes position is a property of enumeration.
It is the reverse. Iterators is secondary to the order. Iterator walks
pairs in the order of pairs = in the order their positions.
You have some problem with an iterator
interface as opposed to an array interface??
Yes, I am against pointers (referential semantics) in general.
I don't see anything that is not already there. What are reasons for not providing:
M (n) [ e.g. M (n).Key, M (n).Value ]
M (n1..n2) [ in mutable contexts too ]
M'First
M'Last
M1 & M2 [ M1 or M2 ]
They are all well-defined and useful operations.
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:umv8rg$2b4on$1@dont-email.me...
...
It is same benefit Ada arrays have over C's T* pointers and arithmetic of. >> Cursor is merely a fat pointer.
A cursor is an abstract reference. It *might* be implemented with a pointer or with an array index. Indeed, the bounded containers pretty much have to
be implemented with an underlying array.
It would be nice if there was some terminology for abstract references that hadn't been stolen by some programming language. Terms like "pointer" and "access" and "reference" all imply an implementation strategy. That's not relevant most of the time, and many programming language design mistakes follow from that. (Anonymous access types come to mind).
It is same benefit Ada arrays have over C's T* pointers and arithmetic of. Cursor is merely a fat pointer.
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:umotm2$18lqm$1@dont-email.me...
...
Only as far as there is an order implied by the order that things are
returned. That order doesn't have any meaning, and certainly there isn't >>> any
such thing as "forward" or "reverse" to it. (Which was the original
claim,
after all.) There is no "natural" order to the key/element pairs; they
are
effectively unordered.
Iteration = order. It is the same thing. If you provide iteration of pairs >> in the mapping by doing so you provide an order of.
Certainly not. An iteration presents all of the elements in a container, but there is no requirement that there is an order.
Indeed, logically, all of
the elements are presented at the same time (and parallel iteration provides an approximation of that).
If you try to enforce an order on things that don't require it, you end up preventing useful parallelism (practically, at least, no one has succeeded
at providing useful parallelism to sequential code and people have been trying for about 50 years -- they were trying when I was a university
student in the late 1970s).
It always does sense *IF* enumeration (needed for iteration) is
provided.
Enumeration of pairs (<key>, <value>) is not same as ordering values by >>>> the keys.
True, but it doesn't imply any particular ordering. Certainly, no concept >>> of
"forward" or "reverse" applies to such an ordering (nor any stability
requirement).
It does. You have a strict total order of pairs which guarantees existence >> of previous and next pairs according to.
Again, this is unrelated. Iteration can usefully occur in unordered containers (that is, "foreach").
Ordering is a separate concept, not always
needed (certainly not in basic structures like maps, sets, and bags).
Yes position is a property of enumeration.
Surely not. This is a basis for my disagrement with you here.
The only
requirement for enumeration is that all elements are produced.
The order is
an artifact of doing it an inherently parallel operation sequentally.
You have some problem with an iterator
interface as opposed to an array interface??
Yes, I am against pointers (referential semantics) in general.
This is nonsense - virtually everything is referential semantics (other than components). Array indexes are just a poor mans pointer (indeed, I learned how to program in Fortran 66 initially, and way one built useful data structures was to use array indexes as stand-ins for pointers). In A(1), 1
is a reference to the first component of A.
So long as you are using arrays, you are using referential semantics. The only way to avoid it is to directly embed an object directly in an enclosing object (as in a record), and that doesn't work for many problems.
I don't see anything that is not already there. What are reasons for not
providing:
M (n) [ e.g. M (n).Key, M (n).Value ]
M (n1..n2) [ in mutable contexts too ]
M'First
M'Last
M1 & M2 [ M1 or M2 ]
They are all well-defined and useful operations.
Performance.
If all of these things are user-definable, then one has to use
subprogram calls to implement all of them. That can be very expensive, particularly in the case of mutable operations (and mutable slices are the worst of all).
Moreover, since one would want the ability to have generic
and runtime parameters that only meet this interface (and the ability to
pass slices to subprograms that take unconstrained array parameters), you would have to be able to pass all of these subprograms along with
parameters, even when you don't need them. That would make array operations far more expensive than they are today.
I think it is much better to get rid of most of these operations as built-in things and just let the programmer build their own operations as needed.
That keeps the cost confined to those who use them. Distributed overhead is the worst kind, and slices in particular have a boatload of that overhead.
On 2024-01-03 04:15, Randy Brukardt wrote:...
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:umotm2$18lqm$1@dont-email.me...
The meaning of the word "iterate" is doing something (e.g. visiting an element) again. That *is* an order.
Indeed, logically, all of
the elements are presented at the same time (and parallel iteration
provides
an approximation of that).
Parallel iteration changes nothing because involved tasks are enumerated
and thus ordered as well.
If you try to enforce an order on things that don't require it, you end
up
preventing useful parallelism (practically, at least, no one has
succeeded
at providing useful parallelism to sequential code and people have been
trying for about 50 years -- they were trying when I was a university
student in the late 1970s).
Ordering things does not prevent parallelism.
Ordering is a separate concept, not always
needed (certainly not in basic structures like maps, sets, and bags).
Right. But no ordering means no iteration, no foreach etc. If I can
iterate, that I can create an ordered set of (counter, element) pairs.
Done.
Yes position is a property of enumeration.
Surely not. This is a basis for my disagrement with you here.
Then you are disagreeing with core mathematics... (:-))
The order is
an artifact of doing it an inherently parallel operation sequentally.
Yes, ordering is an ability to enumerate elements of a set. It is not an artifact it is the sole semantics of.
So long as you are using arrays, you are using referential semantics. The
only way to avoid it is to directly embed an object directly in an
enclosing
object (as in a record), and that doesn't work for many problems.
The key difference is that index does not refer any element. It is
container + index that do.
From the programming POV it is about avoiding hidden states when you try
to sweep the container part under the rug.
I don't see anything that is not already there. What are reasons for not >>> providing:
M (n) [ e.g. M (n).Key, M (n).Value ]
M (n1..n2) [ in mutable contexts too ]
M'First
M'Last
M1 & M2 [ M1 or M2 ]
They are all well-defined and useful operations.
Performance.
Irrelevant so long it does not tamper implementations of other operations.
If all of these things are user-definable, then one has to use
subprogram calls to implement all of them. That can be very expensive,
particularly in the case of mutable operations (and mutable slices are
the
worst of all).
But better, faster, safer when implemented ad-hoc by the programmer?
I think it is much better to get rid of most of these operations as
built-in
things and just let the programmer build their own operations as needed.
Well, if you'd proposed throwing containers out the standard library I
would believe that you believe in that... (:-))
That keeps the cost confined to those who use them. Distributed overhead
is
the worst kind, and slices in particular have a boatload of that
overhead.
Usability always trumps performance.
And again, looking at the standard containers and all these *tagged* *intermediate* objects one needs in order to do elementary things, I kind
of in doubts... (:-))
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:un3bg9$35mhv$1@dont-email.me...
Yes, ordering is an ability to enumerate elements of a set. It is not an
artifact it is the sole semantics of.
Iteration is not necessarily enumeration. It is applying an operation to all elements, and doing that does not require an order.
The key difference is that index does not refer any element. It is
container + index that do.
That's not a "key difference". That exactly how one should use cursors, especially in Ada 2022. The Ada containers do have cursor-only operations, but those should be avoided since it is impossible to provide useful contracts for those operations (the container is unknown, so the world can
be modified, which is bad for parallelism and understanding). Best to consider those operations obsolete. (Note that I was *always* against the cursor-only operations in the containers.)
So, using a cursor implies calling an operation that includes the container of its parameter.
I don't see anything that is not already there. What are reasons for not >>>> providing:
M (n) [ e.g. M (n).Key, M (n).Value ]
M (n1..n2) [ in mutable contexts too ]
M'First
M'Last
M1 & M2 [ M1 or M2 ]
They are all well-defined and useful operations.
Performance.
Irrelevant so long it does not tamper implementations of other operations.
Exactly. These operations, especially slicing, have a huge impact on the
cost of parameter passing for arrays (whether or not they are used). And that's a pretty fundamental operation.
Specifically, the containers are separate from Ada.
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
And again, looking at the standard containers and all these *tagged*
*intermediate* objects one needs in order to do elementary things, I kind
of in doubts... (:-))
The standard containers were designed to make *safe* containers with decent performance.
Exactly. These operations, especially slicing, have a huge impact on the
cost of parameter passing for arrays (whether or not they are used). And
that's a pretty fundamental operation.
It is not slicing it is dynamically constrained arrays which are required anyway. A general problem of language design is how to treat statically
known constraints effectively.
Ada arrays are pretty good to me. Note, I am saying that after years of
using Ada arrays for interfacing C! Yes, I would like having more support
for flattening arrays, but the mere fact that Ada can interface C using *in-place* semantics invalidates your point.
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I wrote an article on this topic a year and a half ago that I wanted to publish on Ada-Auth.org. But I got enough pushback about not being "neutral" that I never did so. (I don't think discussing why we don't do things some other languages do is negative, but whatever.) I've put this on RR's blog at http://www.rrsoftware.com/html/blog/consequences.html so it isn't lost.
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:un64o3$3krch$1@dont-email.me...
...
Exactly. These operations, especially slicing, have a huge impact on the >>> cost of parameter passing for arrays (whether or not they are used). And >>> that's a pretty fundamental operation.
It is not slicing it is dynamically constrained arrays which are required
anyway. A general problem of language design is how to treat statically
known constraints effectively.
No, it's the combination of slicing and passing arrays with unknown (at compile-time) constraints that causes problems.
And it only causes problems
if you want to separate the array interface and the array implementation (which we both want to do). In such a case, you are passing arrays with unknown constraints and implementation. Assignable slices don't work with that, as they require a contiguous implementation of elements.
Inferfacing is using the array implementation, not the array interface. Of course it works great, as you note Ada commingles those in a way that makes them inseparable. To separate them, you are going to have to lose something.
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I would tend to argue that it is indeed the case that you get dubious
results when you put usability first. Ada puts
readability/understandability, maintainability, and consistency first (along with performance). Those attributes tend to provide usability, but not at
the cost of making things less consistent or understandable.
I wrote an article on this topic a year and a half ago that I wanted to publish on Ada-Auth.org. But I got enough pushback about not being "neutral" that I never did so. (I don't think discussing why we don't do things some other languages do is negative, but whatever.) I've put this on RR's blog at http://www.rrsoftware.com/html/blog/consequences.html so it isn't lost.
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:un64o3$3krch$1@dont-email.me...
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I would tend to argue that it is indeed the case that you get dubious
results when you put usability first. ... http://www.rrsoftware.com/html/blog/consequences.html
On Thu, 4 Jan 2024 20:00:37 -0600, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:un64o3$3krch$1@dont-email.me...
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I would tend to argue that it is indeed the case that you get dubious
results when you put usability first. ...
http://www.rrsoftware.com/html/blog/consequences.html
Without reading that, I would never have understood "usability" to mean
"ease of writing". I learned from early on in my programming career that readability was more important than writability. So "using" a language doesn't end with writing the code: you then have to test and debug it-- basically lick it into shape--then maintain it afterwards.
"Lawrence D'Oliveiro" <ldo@nz.invalid> wrote in message news:unafcg$bpv5$7@dont-email.me...
On Thu, 4 Jan 2024 20:00:37 -0600, Randy Brukardt wrote:
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:un64o3$3krch$1@dont-email.me...
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I would tend to argue that it is indeed the case that you get dubious
results when you put usability first. ...
http://www.rrsoftware.com/html/blog/consequences.html
Without reading that, I would never have understood "usability" to mean
"ease of writing". I learned from early on in my programming career that
readability was more important than writability. So "using" a language
doesn't end with writing the code: you then have to test and debug it--
basically lick it into shape--then maintain it afterwards.
Usability is of course not just ease-of-writing, but a lot of people tend to co-mingle the two. For readability, too little information can be just as
bad as too much. For writability, the less you have to write, the better.
On 2024-01-05 03:00, Randy Brukardt wrote:...
Thanks for posting this.
I disagree with what you wrote on several points:
1. Your premise was that use = writing. To me using includes all aspects
of software developing and maintenance process. Writing is only a small
part of it.
2. You argue for language regularity as if it were opposite to usability. Again, it is pretty much obvious that a regular language is easier to use
in any possible sense.
3. Removing meaningless repetitions contributes to usability. But X := X +
Y is only one instance where Ada required such repetition. There are
others. E.g.
if X in T'Class then
declare
XT : T'Class renames T'Class (X);
T'Class is repeated 3 times. A discussion point is whether a new name XT could be avoided etc.
Introducing @ for a *single* purpose contradicts the principle of
regularity. I would rather have a regular syntax for most if not all such instances.
For writability, the less you have to write, the better.
Usability is of course not just ease-of-writing, but a lot of people tend to co-mingle the two. For readability, too little information can be just as
bad as too much. For writability, the less you have to write, the better.
@ is regular in the sense that it is allowed anywhere in an expression. If you tried to expand the use to other contexts, you would have to differentiate them, which would almost certainly require some sort of declaration. But doing that risks making the mechanism as wordy as what it replaces (which obviously defeats the purpose).
We looked at a number of ideas like that, but they didn't seem to help comprehension. In something like:
LHS:(X(Y)) := LHS + 1;
(where LHS is an arbitrary identifier), if the target name is fairly long,
it could be hard to find where the name for the target is given, and in any case, it adds to the name space that the programmer has to remember when reading the source expression. That didn't seem to add to readability as
much as the simple @ does.
In any case, these things are trade-offs, and certainly nothing is absolute. But @ is certainly much more general than ":=+" would be, given that it
works with function calls and array indexing and attributes and user-defined operations rather than just a single operator.
For the 9X and 0X revisions I suggested adding "when <condition>" to
return and raise statements, similar to its use on exit statements. This
was rejected because the language already has a way to accomplish this: if statements.
Given that one can do
declare
V : T renames Very_Long_Identifier;
begin
V := V - 23;
end;
it seems that @ should also have been rejected. Probably more so, since @
is completely new syntax rather than reusing existing syntax on some additional statements. What is the justification of accepting @ while
still rejecting the other?
--
Jeff Carter
"If I could find a sheriff who so offends the citizens of Rock
Ridge that his very appearance would drive them out of town ...
but where would I find such a man? Why am I asking you?"
Blazing Saddles
37
OTOH, we added "when condition" to loops (which I thought
was unnecessary, but I lost that) ...
"Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not> wrote in message news:uneel2$12ufr$1@dont-email.me...
I don't recall ever seriously considering this (might just my memory getting old). I suspect that didn't get rejected so much as not making the cut as important enough.
Le 06/01/2024 03:03, Randy Brukardt a crit:
Usability is of course not just ease-of-writing, but a lot of people tend toYes, I'm always surprised to see many languages (including Rust)
co-mingle the two. For readability, too little information can be just as bad as too much. For writability, the less you have to write, the better.
praising themselves of being "concise". Apart from saving some
keystrokes, I fail to see the benefit of being concise...
Yes, I'm always surprised to see many languages (including Rust)
praising themselves of being "concise". Apart from saving some
keystrokes, I fail to see the benefit of being concise...
"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:un64o3$3krch$1@dont-email.me...[. . .]
...
Usability always trumps performance.
That's the philosophy of languages like Python, not Ada.
Ah, this is why Python is totally unusable? (:-))
I would tend to argue that it is indeed the case that you get dubious
results when you put usability first. Ada puts
readability/understandability, maintainability, and consistency first
(along
with performance). Those attributes tend to provide usability, but not at
the cost of making things less consistent or understandable.
I wrote an article on this topic a year and a half ago that I wanted to publish on Ada-Auth.org. But I got enough pushback about not being
"neutral"
that I never did so. (I don't think discussing why we don't do things some other languages do is negative, but whatever.) I've put this on RR's blog
at
http://www.rrsoftware.com/html/blog/consequences.html so it isn't lost.
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