Lambda with specified template type parameter does not work with IFTI

[dlangBugzillaToGithub]

Ali Ak reported this on 2017-12-06T10:40:16Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=18037

CC List

• Steven Schveighoffer (@schveiguy)

Description

When you declare a template lambda:

immutable lambda(T) = (T n) => n * n;

and call it without an explicit type it errors with with:

lambda cannot deduce function from argument types !()(int)

auto x = lambda!int(2); // works
auto x = lambda(2); // not works

Is this a bug? - tired on dmd v2.077.1

[dlangBugzillaToGithub]

schveiguy (@schveiguy) commented on 2017-12-06T15:43:47Z

Tested back to 2.070.0, which is where short lambda syntax was introduced. Still fails.

The immutable looks odd, but even with alias this doesn't work.

alias lambda(T) = (T n) => n * n;

should expand to:

template lambda(T)
{
    alias lambda = (T n) => n * n;
}

Neither of these successfully use IFTI.

However, these all work:

alias lambda = (int n) => n * n;
alias lambda = n => n * n;