Bug 14600 – Lambda with body allowed as template alias argument

When run, the following program compiles without error but produces no output. void test(alias d)() { d(); } void main() { import std.stdio : writeln; test!(() => { writeln("testing"); }); } Compare to the following code, which does not compile because the => syntax is only supposed to work with simple expressions. void test(void delegate() d) { d(); } void main() { import std.stdio : writeln; test(() => { writeln("testing"); }); } Maybe the restriction on the => syntax not allowing bracketed expressions should be lifted. I've spotted code on github that assumes this style does actually work.

it's actually a grammar issue. what `() => { writeln("testing"); }` does is returns `void delegate () { writeln("testing"); }`. i.e. `=> { writeln("testing"); }` is correctly parsed as *expression* which returns delegate. another thing is that compiler doesn't emit warnings by default. compiling the code with "-w" flag gives this message: Warning: calling z01.main.__lambda1 without side effects discards return value of type void function() @safe, prepend a cast(void) if intentional i think that the report can be closed as "not-a-bug". we'd better spam bugzilla with "make warnings opt-out instead of opt-in" requests. ;-)

You're right. I should have tested with -w.