On Tuesday, 27 February 2018 at 20:51:25 UTC, ag0aep6g wrote:
On 02/27/2018 09:30 PM, Radu wrote:
enum Type { a };
struct S(Type t = Type.a)
{
this(Type)(Type t)
{
import std.stdio;
writeln("ctor called.");
}
}
void main()
{
auto x = S!(Type.a)(Type.a);
void* y = &x;
auto z = (cast(S!(Type.a)) y);
}
Surprisingly the cast will actually call the ctor. Is this to
be expected? Sure looks like a bug to me, as a non templated S
will complain about the cast.
Not a bug. The spec says [1]: "Casting a value v to a struct S,
when value is not a struct of the same type, is equivalent to:
S(v)"
Templates have nothing to do with it. Your code boils down to
this:
----
struct S
{
this(void* t)
{
import std.stdio;
writeln("ctor called.");
}
}
void main()
{
void* y;
auto z = cast(S) y;
}
----
[1] https://dlang.org/spec/expression.html#cast_expressions
OK, got it - thanks.
But this:
struct S
{
this(int t)
{
import std.stdio;
writeln("ctor called.");
}
}
void main()
{
auto x = S(1);
void* y = &x;
auto z = (cast(S) y);
}
Produces:
Error: cannot cast expression y of type void* to S
Which is kinda correct as I don't have any ctor in S taking a
void*.
Adding
this(void* t)
{
import std.stdio;
writeln("ctor called.");
}
Will make the error go away.
So the bug is that somehow the templated version makes it so
there is an implicit void* ctor.
