Implicit Template Parameters

Question

The following code generates a compile error in Xcode:

template 
struct Foo
{
    Foo(T Value)
    {
    }
};

int main()
{
    Foo MyFoo(123);         


        

Answer 1

Compiler can deduce the template argument such case:

template
void fun(T param)
{
    //code...
}

fun(100);    //T is deduced as int;
fun(100.0);  //T is deduced as double
fun(100.0f); //T is deduced as float

Foo foo(100);
fun(foo);    //T is deduced as Foo;

Foo bar('A');
fun(bar);    //T is deduced as Foo;

Actually template argument deduction is a huge topic. Read this article at ACCU:

The C++ Template Argument Deduction