Bug 9831 – Error message with failed lambda inference

void main() { immutable int c; int function(int x) func; func = x => c; } DMD 2.063alpha gives the error: temp.d(4): Error: cannot infer function literal type from int function(int x) But I expect an error similar to other cases of unfit lambdas, similar to: test.d(4): Error: cannot implicitly convert expression (__lambda1) of type int delegate(int) nothrow pure @safe to int function(int).

x => c does not have a type yet, the problem is in inferring the type, not converting. I'm tempted to close as invalid, but I'll leave it up to you.

(In reply to comment #1) > x => c does not have a type yet, the problem is in inferring the type, not > converting. > > I'm tempted to close as invalid, but I'll leave it up to you. Dropping the immutable annotation, this simpler program gives (dmd 2.065alpha): void main() { int c; int function(int x) func; func = x => c; } temp.d(4): Error: cannot infer function literal type from int function(int x) While if I copy the value of 'c' inside the lambda it compiles with no errors: void main() { int c; int function(int x) func; func = x => 0; } So I think this issue is valid, the type inferencer could become a bit smarter and compile the first case too. But perhaps this issue should be regarded as an Enhancement.

(In reply to comment #2) > > So I think this issue is valid, the type inferencer could become a bit smarter > and compile the first case too. But perhaps this issue should be regarded as an > Enhancement. What makes you think the first case is valid? void main() { immutable int c; // immutable local variable int function(int x) func; func = x => c; // needs context to access c } What exactly would you expect to happen? A similar case: void main(string[] args) { immutable int c = args.length; int function(int x) func; func = x => c; }

(In reply to comment #0) > void main() { > immutable int c; > int function(int x) func; > func = x => c; > } > > DMD 2.063alpha gives the error: > > temp.d(4): Error: cannot infer function literal type from int function(int x) I can agree that the current error message does not have so many information, but > But I expect an error similar to other cases of unfit lambdas, similar to: > > test.d(4): Error: cannot implicitly convert expression (__lambda1) of type int > delegate(int) nothrow pure @safe to int function(int). the op code should produce "__lambda1 cannot access frame of function D main" error, because required type is function pointer, not delegate. https://github.com/D-Programming-Language/dmd/pull/2798

(In reply to comment #3) > What makes you think the first case is valid? > > void main() { > immutable int c; // immutable local variable > int function(int x) func; > func = x => c; // needs context to access c > } > > What exactly would you expect to happen? Right, I was wrong, sorry. (In reply to comment #4) > the op code should produce "__lambda1 cannot access frame of function D main" > error, because required type is function pointer, not delegate. > > https://github.com/D-Programming-Language/dmd/pull/2798 Thank you, the new error message is good and helps me avoid similar mistakes.

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/a291c08cd5432419ad9c6a12e6e6e00b9320b586 fix Issue 9831 - Error message with failed lambda inference https://github.com/D-Programming-Language/dmd/commit/e6204b268161fdf7fc95a1ccab304803b3493c86 Merge pull request #2798 from 9rnsr/fix9831 Issue 9831 - Error message with failed lambda inference