Implicit Template Parameters

The following code generates a compile error in Xcode:

template <typename T>
struct Foo
{
    Foo(T Value)
    {
    }
};

int main()
{
    Foo MyFoo(123);
    return 0;
}

error: missing template arguments before 'MyFoo'

Changing Foo MyFoo(123); to Foo<int> MyFoo(123); fixes the issue, but shouldn't the compiler be able to figure out the appropriate datatype?

Is this a compiler bug, or am I misunderstanding implicit template parameters?