Question

Why this is an Error ?

float (^isFloat)(float) = ^(float d)
{
    return d*2.0;
};

At the sometime, the following is error free,

float (^isFloat)(float) = ^(float d)
{
    return d;
};

PLease help me understand.

Answer 1

Because your return type on the first block is incorrect.

You defined the block to return a float, but you multiplied a float by a double. If you change it to d * 2.0f everything should work just fine.