import std.stdio;
import std.range : chain;

auto test(string a) {
    return test(a, "b");
}

auto test(string a, string b) {
    return chain(a, b);
}

void main() {
    writeln(test(a));
}

Ends with: Error: forward reference to inferred return type of function call 'test'

I know this exact sample is solvable by default parameter but there are cases where it is not possible. What to do then?

On Tuesday, 25 August 2015 at 18:19:40 UTC, tchaloupka wrote:
> import std.stdio;
> import std.range : chain;
>
> auto test(string a) {
>     return test(a, "b");
> }
>
> auto test(string a, string b) {
>     return chain(a, b);
> }
>
> void main() {
>     writeln(test(a));
> }
>
> Ends with: Error: forward reference to inferred return type of function call 'test'
>
> I know this exact sample is solvable by default parameter but there are cases where it is not possible. What to do then?

I think this is a bug, but is easily worked around with:

auto test(string a) {
    return .test(a, "b");
}

I suspect that the reason the error occurs, is that the auto return type automatically rewrites the function declaration into an eponymous template declaration. Since this creates a new naming scope, "test" by itself will only match the declaration inside the eponymous template. Forcing the compiler to look on the module level will force it to perform overload resolution.

On Tuesday, 25 August 2015 at 18:29:08 UTC, Vladimir Panteleev wrote:
>
> I think this is a bug, but is easily worked around with:
>
> auto test(string a) {
>     return .test(a, "b");
> }
>

Thanks, this worked.
Filled it: https://issues.dlang.org/show_bug.cgi?id=14965

On 08/25/2015 08:29 PM, Vladimir Panteleev wrote:
>
> I think this is a bug, but is easily worked around with:
>
> auto test(string a) {
>      return .test(a, "b");
> }
>
> I suspect that the reason the error occurs, is that the auto return type
> automatically rewrites the function declaration into an eponymous
> template declaration.  ...

No true. In fact, doing so manually works around the problem. :o)

This compiles and runs:

import std.stdio;
import std.range : chain;

auto test()(string a) {
    return test(a,"b");
}

auto test(string a,string b) {
    return chain(a,b);
}

void main() {
    writeln(test("a"));
}

On 08/26/2015 09:55 PM, Timon Gehr wrote:
> On 08/25/2015 08:29 PM, Vladimir Panteleev wrote:
>>
>> I think this is a bug, but is easily worked around with:
>>
>> auto test(string a) {
>>      return .test(a, "b");
>> }
>>
>> I suspect that the reason the error occurs, is that the auto return type
>> automatically rewrites the function declaration into an eponymous
>> template declaration.  ...
>
> No true. In fact, doing so manually works around the problem. :o)
>
> This compiles and runs:
>
> import std.stdio;
> import std.range : chain;
>
> auto test()(string a) {
>      return test(a,"b");
> }
>
> auto test(string a,string b) {
>      return chain(a,b);
> }
>
> void main() {
>      writeln(test("a"));
> }

Another workaround is to order the declarations in the opposite way:

import std.stdio;
import std.range : chain;

auto test(string a,string b) {
    return chain(a,b);
}
auto test(string a) {
    return test(a,"b");
}
void main() {
    writeln(test("a"));
}

On Wednesday, 26 August 2015 at 20:02:35 UTC, Timon Gehr wrote:
> Another workaround is to order the declarations in the opposite way:
>
> import std.stdio;
> import std.range : chain;
>
> auto test(string a,string b) {
>     return chain(a,b);
> }
> auto test(string a) {
>     return test(a,"b");
> }
> void main() {
>     writeln(test("a"));
> }

It's definitely a bug if the code is dependent on order of declaration.