Why Does \"Foo me;\" Not Work with Default Template Arguments in C 11?

Overcoming Explicit Argument Specification for Class Templates with Default Template Arguments

C 11 introduced default template arguments, a concept that initially sparked confusion. This article delves into this topic and explains why an instance of a class template with default template arguments, such as "Foo me;", is not valid in main.

Consider the following class template with a default template argument of int:

template <typename T = int>
class Foo {};

Despite the presence of the default template argument, the code "Foo me;" in main results in a compilation error. This is because empty angle brackets, as in "Foo<> me;", are required to explicitly specify the default template argument.

The reason behind this requirement is the need for a consistent syntax with function calls. In C , a function with a default argument requires the argument syntax to be present, even if the default value is used. This rule extends to class templates with default template arguments, ensuring consistency in language syntax.

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