Is the `inline` Keyword Meaningless in C Templates?

Using Inline Keyword with Templates: Is It Meaningless?

In C , the inline keyword suggests that a function should be inlined by the compiler if possible. However, given that templates are defined within headers, and modern compilers can determine if inlining is beneficial, one may wonder if the inline keyword becomes redundant.

The Power of Explicit Specialization

The C standard clarifies that not all function templates are inline by default. When specializing a function template (providing an explicit implementation for specific parameter types), the use of inline becomes crucial. Failure to specify inline for a full specialization can lead to errors, as seen in the following example:

tpl.h

template<class T> void f(T);
template<class T> inline T g(T);

template<> inline void f<>(int);  // Explicit specialization of f
template<> int g<>(int);  // Error: g<> is not inline

Consistency and Clarity

Although the inline keyword is not strictly necessary for non-fully specialized function templates, consistency and clarity are valuable principles. By explicitly stating inline, you convey your intention to the compiler and other developers. This reduces confusion and makes code more maintainable.

Key Takeaways

In summary, omitting inline for non-fully specialized function templates is allowable but can lead to issues. For full specializations, inline is mandatory. A consistent approach is to use inline whenever you intend for a function to be inlined. This ensures that your code is clear, correct, and aligns with best practices.

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