Comment #0 by bearophile_hugs — 2011-09-13T04:18:51Z
In the following D2 program only the Mfoo1 compiles:
import std.functional: memoize;
struct Foo1 {
int x;
static Foo1 opCall(int x_) {
Foo1 f;
f.x = x_;
return f;
}
}
struct Foo2 {
int x;
}
struct Foo3 {
int x;
this(int x_) {
this.x = x_;
}
}
void main() {
alias memoize!Foo1 Mfoo1;
alias memoize!Foo2 Mfoo2;
alias memoize!Foo3 Mfoo3;
}
DMD 2.055 gives errors like:
...\src\phobos\std\traits.d(128): Error: static assert "argument has no return type"
...\src\phobos\std\functional.d(713): instantiated from here: ReturnType!(Foo2)
test.d(21): instantiated from here: memoize!(Foo2)
...\src\phobos\std\traits.d(128): Error: static assert "argument has no return type"
...\src\phobos\std\functional.d(713): instantiated from here: ReturnType!(Foo3)
test.d(22): instantiated from here: memoize!(Foo3)
The static assert is in std.traits:
template ReturnType(/+@@@BUG4217@@@+/func...)
if (/+@@@BUG4333@@@+/staticLength!(func) == 1)
{
static if (is(FunctionTypeOf!(func) R == return))
alias R ReturnType;
else
static assert(0, "argument has no return type");
}
I think Mfoo2 and Mfoo3 too should compile. Writing Foo2(5) is like calling the function Foo2 with argument x = 5, and returning a struct Foo2 result. I think this is a place where telling apart structs and functions is an artificial distinction that is the opposite of useful.
See one use case:
http://www.digitalmars.com/webnews/newsgroups.php?art_group=digitalmars.D&article_id=144333
Comment #1 by robert.schadek — 2024-12-01T16:14:21Z