http://dlang.org/phobos/std_stdio.html#.File.readf

The example code is:

void main()
{
    import std.stdio;
    auto f = File("input");
    foreach (_; 0 .. 3)
    {
        int a;
        f.readf!" %d"(a);
        writeln(++a);
    }
}

and does not compile:

test.d(8): Error: template instance std.stdio.File.readf!" %d" does not match template declaration readf(Data...)(in char[] format, Data data) if (allSatisfy!(isPointer, Data))