Re: Cannot always deduce template arguments when using implicitly cast array literals
On Friday, 23 July 2021 at 13:53:27 UTC, Rekel wrote:
As one can see, implicitly casting array literals in templates
works fine in the case of bar, as does explicit use of
templates in the case of foo, but for some reason foo does not
manage to deduce its arguments like bar does.
Interestingly enough, I ran into the same issue recently, but
with a much simpler piece of code:
```d
module app;
import std.stdio;
struct One(T, uint L) {
T[L] array;
bool opEquals(T2)(const T2[L] rhs) const {
return true;
}
}
struct Two(T, uint L) {
T[L][L] array;
bool opEquals(T2)(const T2[L][L] rhs) const {
return true;
}
}
void foo() {
auto a = One!(float, 2)([1, 2]);
int[2] b = [1, 2];
writeln(a == b); // True
writeln(a.array == b); // True
writeln(a == [1, 2]); // True
writeln(a.array == [1, 2]); // True
}
void bar() {
auto a = Two!(float, 2)([[1, 2], [3, 4]]);
int[2][2] b = [[1, 2], [3, 4]];
writeln(a == b); // True
writeln(a.array == b); // True
writeln(a == [[1, 2], [3, 4]]); // cannot deduce function from
argument types `!()(int[][])`
writeln(a.array == [[1, 2], [3, 4]]); // True
}
void main(){
foo();
bar();
}
```
I'd love to know if there's any plans on changing/fixing this. I
haven't been able to find any mention of it apart from in this
thread.
Kind regards,
~ HN
(/Rekel: name change & account loss. It'd be nice if the forum
supported editing & profiles (including posts/comments or at
least login credential retrieval (like https://code.dlang.org/
does))
Re: Cannot always deduce template arguments when using implicitly cast array literals
On Friday, 23 July 2021 at 14:41:41 UTC, Paul Backus wrote: The first is to change the type of right from const R to const T[L1], which removes the type specialization: Thanks for suggesting that fix, removing R altogether is a very simple solution I hadn't considered. :) Unfortunately, the algorithm it uses for this is not very sophisticated, and does not take type specializations (like `R : T[L1]`) into account. This seems like a slight oversight to me, do you know if there would be any chance of this changing in the future?
Re: Cannot always deduce template arguments when using implicitly cast array literals
On Friday, 23 July 2021 at 13:53:27 UTC, Rekel wrote:
After simplifying a part of my code I found the following code
cannot deduce the template arguments, but I have no clue why.
```d
void foo(L : T[L1][L2], uint L1, uint L2, T, R:
T[L1])(const L left, const R right) {
// Function
}
void bar(uint L)(float[L] l) {
// Function
}
void main(string[] args) {
bar([1.0f, 2, 3, 4, 5, 6, 7, 8]); // implicitly cast to
float[8], works
float[4][1] l = [[1, 2, 3, 4]];
foo!(typeof(l), 4, 1, float, float[4])(l, [1.0f, 2, 3, 4]); //
also works
foo(l, [1.0f, 2, 3, 4]); // cannot deduce function from
argument types (?)
}
```
As one can see, implicitly casting array literals in templates
works fine in the case of bar, as does explicit use of
templates in the case of foo, but for some reason foo does not
manage to deduce its arguments like bar does.
Looks like the problem is that the compiler is interpreting
`[1.0f, 2, 3, 4]` as a dynamic array (`float[]`) instead of a
static array (`float[4]`).
Array literals are treated as dynamic arrays by default, and as
static arrays only in specific contexts where the compiler is
able to determine that a static array is required. Unfortunately,
the algorithm it uses for this is not very sophisticated, and
does not take type specializations (like `R : T[L1]`) into
account.
There are two ways you can solve this. The first is to change the
type of `right` from `const R` to `const T[L1]`, which removes
the type specialization:
```d
void foo(L : T[L1][L2], uint L1, uint L2, T)
(const L left, const T[L1] right)
{
// Function
}
```
The second is to use `std.array.staticArray` to manually cast the
array literal to a static array:
```d
import std.array: staticArray;
foo(l, staticArray!([1.0f, 2, 3, 4]));
```
Cannot always deduce template arguments when using implicitly cast array literals
After simplifying a part of my code I found the following code
cannot deduce the template arguments, but I have no clue why.
```d
void foo(L : T[L1][L2], uint L1, uint L2, T, R:
T[L1])(const L left, const R right) {
// Function
}
void bar(uint L)(float[L] l) {
// Function
}
void main(string[] args) {
foo2([1.0f, 2, 3, 4, 5, 6, 7, 8]); // implicitly cast to
float[8], works
float[4][1] l = [[1, 2, 3, 4]];
foo!(typeof(l), 4, 1, float, float[4])(l, [1.0f, 2, 3, 4]); //
also works
foo(l, [1.0f, 2, 3, 4]); // cannot deduce function from argument
types (?)
}
```
As one can see, implicitly casting array literals in templates
works fine in the case of bar, as does explicit use of templates
in the case of foo, but for some reason foo does not manage to
deduce its arguments like bar does.
The type of l is well known, and given the template, the type of
R should thus be known as well. T[L1] should be deduced to
float[4].
Did I make a mistake in the argument list? I know things like the
order are sometimes issues, but that seems fine to me here.
Seeing as bar functions fine (as does foo when R and right are
removed) I'm at a loss.
Thanks you in advance!
