TDPL: Function literals with missing argument type specifiers do not compile

[Andrej Mitrovic]

The following example should compile according to TDPL. The compiler is supossed to automatically infer the type of the parameter in the function literal:

void main() { }

T[] find(alias pred, T)(T[] input)
    if (is(typeof(pred(input[0])) == bool))
{
    for (; input.length > 0; input = input[1 .. $])
    {
        if (pred(input[0]))
            break;
    }
    return input;
}

unittest {
    int[] a = [1, 2, 3, 4, -5, 3, -4];
    
    // find first negative number
    auto b = find!(function bool(int x) { return x < 0; })(a);
    auto c = find!(function (x) { return x < 0; })(a);
    auto d = find!((x) { return x < 0; })(a);
}

The auto c and auto d lines are not compiling:
higher_functions.d(55): Error: template higher_functions.find(alias pred,T) if (is(typeof(pred(input[0])) == bool)) does not match any function template declaration
higher_functions.d(55): Error: template higher_functions.find(alias pred,T) if (is(typeof(pred(input[0])) == bool)) cannot deduce template function from argument types !(__funcliteral2)(int[])
higher_functions.d(55): Error: template instance errors instantiating template
higher_functions.d(56): Error: template higher_functions.find(alias pred,T) if (is(typeof(pred(input[0])) == bool)) does not match any function template declaration
higher_functions.d(56): Error: template higher_functions.find(alias pred,T) if (is(typeof(pred(input[0])) == bool)) cannot deduce template function from argument types !(__dgliteral4)(int[])
higher_functions.d(56): Error: template instance errors instantiating template

Gotta love those error messages, a C++ programmer will feel right at home! ;)

 If I add a type specifier like so:

    auto c = find!(function (int x) { return x < 0; })(a);
    auto d = find!((int x) { return x < 0; })(a);

Then it will compile. Should I report this to bugzilla?