digitalmars.D.learn - Array types not treated uniformly when passed as ranges
- jam (47/47) Feb 14 2011 Hi all,
- Steven Schveighoffer (15/61) Feb 15 2011 This is because:
Hi all,
Just curious as to the difference in the built-in variable length
array vs. the std.container.Array and fixed length arrays when it
comes to using them in functions that take Ranges.
For instance the following does not compile:
import std.algorithm;
import std.stdio;
import std.range;
import std.conv;
import std.container;
import std.array;
void main() {
int[5] builtin_fixed;
int[] builtin_variable;
Array!(int) con_array;
con_array.length(5);
builtin_variable.length = 5;
fill(builtin_variable, 9); //ok, no error
isSorted(builtin_variable); //ditto
//The following 4 statements produce errors
fill(builtin_fixed, 9);
fill(con_array, 9);
isSorted(con_array);
isSorted(builtin_fixed);
}
The errors are variations on:
Error: template std.algorithm.fill(Range,Value) if
(isForwardRange!(Range) && is(typeof(range.front = filler))) does not
match any function template declaration
Error: template std.algorithm.fill(Range,Value) if
(isForwardRange!(Range) && is(typeof(range.front = filler))) cannot
deduce template function from argument types !()(int[5LU],int)
If I change those 4 statements to:
fill(builtin_fixed[], 9);
fill(con_array[], 9);
isSorted(con_array[]);
isSorted(builtin_fixed[]);
effectively passing ranges (std.container.Array!(int).Array.Range in
the case of con_array, and int[] for builtin_fixed) which then works
as expected. This all makes sense, and it's easy enough to write
wrappers, but I would (well and I did) expect the first way to just
work. This may just be a nitpick I guess, but being new to the
language this little detour involved quite a bit of time research (not
a bad thing, I did learn quite a bit in the process), but makes me
wonder if I am missing something fundamental regarding when I should
be using these different array types.
Cheers
Feb 14 2011
On Mon, 14 Feb 2011 21:18:39 -0500, jam <gr0v3er gmail.com> wrote:
Hi all,
Just curious as to the difference in the built-in variable length
array vs. the std.container.Array and fixed length arrays when it
comes to using them in functions that take Ranges.
For instance the following does not compile:
import std.algorithm;
import std.stdio;
import std.range;
import std.conv;
import std.container;
import std.array;
void main() {
int[5] builtin_fixed;
int[] builtin_variable;
Array!(int) con_array;
con_array.length(5);
builtin_variable.length = 5;
fill(builtin_variable, 9); //ok, no error
isSorted(builtin_variable); //ditto
//The following 4 statements produce errors
fill(builtin_fixed, 9);
fill(con_array, 9);
isSorted(con_array);
isSorted(builtin_fixed);
}
The errors are variations on:
Error: template std.algorithm.fill(Range,Value) if
(isForwardRange!(Range) && is(typeof(range.front = filler))) does not
match any function template declaration
Error: template std.algorithm.fill(Range,Value) if
(isForwardRange!(Range) && is(typeof(range.front = filler))) cannot
deduce template function from argument types !()(int[5LU],int)
If I change those 4 statements to:
fill(builtin_fixed[], 9);
fill(con_array[], 9);
isSorted(con_array[]);
isSorted(builtin_fixed[]);
effectively passing ranges (std.container.Array!(int).Array.Range in
the case of con_array, and int[] for builtin_fixed) which then works
as expected. This all makes sense, and it's easy enough to write
wrappers, but I would (well and I did) expect the first way to just
work. This may just be a nitpick I guess, but being new to the
language this little detour involved quite a bit of time research (not
a bad thing, I did learn quite a bit in the process), but makes me
wonder if I am missing something fundamental regarding when I should
be using these different array types.
This is because:
1. a fixed-sized array is not a range. It is passed by value, not by
reference. The problem there is IFTI thinking you want to pass the fixed
array as a fixed array and not as a slice.
2. a container is not a range. An Array is a container, so you must
extract a range from it to use it in range-like activities.
The second point seems odd, since builtin arrays are ranges, but an Array
is different because it's a true reference type (changing the length from
one reference alters the length of another reference) and it "owns" the
memory contained within, unlike a builtin array which just references the
memory.
But it's also easy to consider other things. Consider a RedBlackTree
container, should that be a range? What happens when you popFront?
-Steve
Feb 15 2011
jam <gr0v3er+d gmail.com> On Tue, 15 Feb 2011 09:00:54 -0500, Steven Schveighoffer wrote:On Mon, 14 Feb 2011 21:18:39 -0500, jam <gr0v3er gmail.com> wrote:I'm glad I came to the same conclusions on my own after perusing the docs and src files some more. I still find it a bit odd that I'm not testing whether my data structure is sorted or not, but a full-length slice of the structure. Although, I guess when I really think about it, it's not that mechanically different than passing a pair of iterators.Hi all, Just curious as to the difference in the built-in variable length array vs. the std.container.Array and fixed length arrays when it comes to using them in functions that take Ranges. For instance the following does not compile: import std.algorithm; import std.stdio; import std.range; import std.conv; import std.container; import std.array; void main() { int[5] builtin_fixed; int[] builtin_variable; Array!(int) con_array; con_array.length(5); builtin_variable.length = 5; fill(builtin_variable, 9); //ok, no error isSorted(builtin_variable); //ditto //The following 4 statements produce errors fill(builtin_fixed, 9); fill(con_array, 9); isSorted(con_array); isSorted(builtin_fixed); } The errors are variations on: Error: template std.algorithm.fill(Range,Value) if (isForwardRange!(Range) && is(typeof(range.front = filler))) does not match any function template declaration Error: template std.algorithm.fill(Range,Value) if (isForwardRange!(Range) && is(typeof(range.front = filler))) cannot deduce template function from argument types !()(int[5LU],int) If I change those 4 statements to: fill(builtin_fixed[], 9); fill(con_array[], 9); isSorted(con_array[]); isSorted(builtin_fixed[]); effectively passing ranges (std.container.Array!(int).Array.Range in the case of con_array, and int[] for builtin_fixed) which then works as expected. This all makes sense, and it's easy enough to write wrappers, but I would (well and I did) expect the first way to just work. This may just be a nitpick I guess, but being new to the language this little detour involved quite a bit of time research (not a bad thing, I did learn quite a bit in the process), but makes me wonder if I am missing something fundamental regarding when I should be using these different array types.This is because: 1. a fixed-sized array is not a range. It is passed by value, not by reference. The problem there is IFTI thinking you want to pass the fixed array as a fixed array and not as a slice. 2. a container is not a range. An Array is a container, so you must extract a range from it to use it in range-like activities. The second point seems odd, since builtin arrays are ranges, but an Array is different because it's a true reference type (changing the length from one reference alters the length of another reference) and it "owns" the memory contained within, unlike a builtin array which just references the memory. -SteveBut it's also easy to consider other things. Consider a RedBlackTree container, should that be a range? What happens when you popFront?Indeed, and operations like fill and isSorted also do not make sense on such containers. However, popFront makes a world of sense for a range representing a traversal. Thanks to both Jonathon and yourself for your help
Feb 15 2011
On 02/15/2011 03:00 PM, Steven Schveighoffer wrote:On Mon, 14 Feb 2011 21:18:39 -0500, jam <gr0v3er gmail.com> wrote:Isn't there a step to pass toward integration of builtin collections and ranges. Should be transparent from the language-side. There are still, I guess, far too many implementation details leaking into language semantics. Python is a model for that. Denis -- _________________ vita es estrany spir.wikidot.comHi all, Just curious as to the difference in the built-in variable length array vs. the std.container.Array and fixed length arrays when it comes to using them in functions that take Ranges. For instance the following does not compile: import std.algorithm; import std.stdio; import std.range; import std.conv; import std.container; import std.array; void main() { int[5] builtin_fixed; int[] builtin_variable; Array!(int) con_array; con_array.length(5); builtin_variable.length = 5; fill(builtin_variable, 9); //ok, no error isSorted(builtin_variable); //ditto //The following 4 statements produce errors fill(builtin_fixed, 9); fill(con_array, 9); isSorted(con_array); isSorted(builtin_fixed); } The errors are variations on: Error: template std.algorithm.fill(Range,Value) if (isForwardRange!(Range) && is(typeof(range.front = filler))) does not match any function template declaration Error: template std.algorithm.fill(Range,Value) if (isForwardRange!(Range) && is(typeof(range.front = filler))) cannot deduce template function from argument types !()(int[5LU],int) If I change those 4 statements to: fill(builtin_fixed[], 9); fill(con_array[], 9); isSorted(con_array[]); isSorted(builtin_fixed[]); effectively passing ranges (std.container.Array!(int).Array.Range in the case of con_array, and int[] for builtin_fixed) which then works as expected. This all makes sense, and it's easy enough to write wrappers, but I would (well and I did) expect the first way to just work. This may just be a nitpick I guess, but being new to the language this little detour involved quite a bit of time research (not a bad thing, I did learn quite a bit in the process), but makes me wonder if I am missing something fundamental regarding when I should be using these different array types.This is because: 1. a fixed-sized array is not a range. It is passed by value, not by reference. The problem there is IFTI thinking you want to pass the fixed array as a fixed array and not as a slice. 2. a container is not a range. An Array is a container, so you must extract a range from it to use it in range-like activities. The second point seems odd, since builtin arrays are ranges, but an Array is different because it's a true reference type (changing the length from one reference alters the length of another reference) and it "owns" the memory contained within, unlike a builtin array which just references the memory. But it's also easy to consider other things. Consider a RedBlackTree container, should that be a range? What happens when you popFront?
Feb 15 2011