Re: Member function passed through template alias only requiring `this` in certain conditions?
On Thursday, 19 July 2018 at 22:16:22 UTC, Ali Çehreli wrote:
On 07/19/2018 08:12 AM, Emma wrote:
> [...]
> If I try to compile it, dmd complains, which I guess makes
sense:
>
> ---
> Error: need this for bar of type void()
> Error: need this for baz of type void()
> ---
>
> [...]
I think it's a compiler bug. The second template argument
should be a lambda as well. When I added the following lines to
test()
pragma(msg, typeof(fn1));
pragma(msg, typeof(fn2));
the output is different:
void delegate() @system
void()
That is for the version of calling test with one lamdba and one
function? (`test!(() => bar, baz)`)
Just a question: The compiler should not automatically convert
those (functions) to lambdas?
Interesting is this:
void test(alias fn1, alias fn2)()
{
pragma(msg, typeof(fn1)); // void delegate() @system
pragma(msg, typeof(fn2)); // void()
fn1();
fn2(); // Error: this for baz needs to be type Boo not type
Foo
}
struct Foo
{
void foo()
{
test!(()=>bar, b.baz);
}
int i = 1337;
struct Boo
{
int j = 3;
void baz()
{writeln(j);}
}
Boo b;
void bar()
{writeln(i);}
}
unittest
{
auto foo = Foo();
foo.foo();
}
Looks like the compiler just assumes the context of the first
delegate to be applicable for the second function?
I think it's a bug probably related to multiple local lambdas.
We had similar issues in the past. Although it works as is, I
recommend you make the second one a lambda as well.
Others, please confirm that it's a bug and let's create a bug
report.
Ali
Re: Member function passed through template alias only requiring `this` in certain conditions?
On 07/19/2018 08:12 AM, Emma wrote:
> void test(alias fn1, alias fn2)()
> {
> fn1();
> fn2();
> }
>
> struct Foo
> {
> void foo()
> {
> test!(bar, baz);
> }
>
> void bar()
> {}
>
> void baz()
> {}
> }
> ---
>
> If I try to compile it, dmd complains, which I guess makes sense:
>
> ---
> Error: need this for bar of type void()
> Error: need this for baz of type void()
> ---
>
> However, if I change line 13 from `test!(bar, baz);` to `test!(() =>
> bar, baz);`, it compiles and executes fine, calling both the `bar` and
> `baz` member functions.
>
> Why is this? Shouldn’t it complain about `baz` needing `this`? Does the
> lambda in the first template argument somehow “pull in” the `this`
> reference for `baz`, too?
>
> Thanks!
I think it's a compiler bug. The second template argument should be a
lambda as well. When I added the following lines to test()
pragma(msg, typeof(fn1));
pragma(msg, typeof(fn2));
the output is different:
void delegate() @system
void()
I think it's a bug probably related to multiple local lambdas. We had
similar issues in the past. Although it works as is, I recommend you
make the second one a lambda as well.
Others, please confirm that it's a bug and let's create a bug report.
Ali
Member function passed through template alias only requiring `this` in certain conditions?
Hello,
I’ve got this piece of code:
---
import std.stdio;
void test(alias fn1, alias fn2)()
{
fn1();
fn2();
}
struct Foo
{
void foo()
{
test!(bar, baz);
}
void bar()
{}
void baz()
{}
}
---
If I try to compile it, dmd complains, which I guess makes sense:
---
Error: need this for bar of type void()
Error: need this for baz of type void()
---
However, if I change line 13 from `test!(bar, baz);` to `test!(()
=> bar, baz);`, it compiles and executes fine, calling both the
`bar` and `baz` member functions.
Why is this? Shouldn’t it complain about `baz` needing `this`?
Does the lambda in the first template argument somehow “pull in”
the `this` reference for `baz`, too?
Thanks!
