How Can I Convert Lambdas to std::function Using Templates in C ?

How to Bridge the Gap: Converting Lambdas to std::function using Templates

Overview

This article addresses the challenge of converting a lambda expression of arbitrary parameters and types into an std::function object using templates. Despite repeated attempts, the author faced obstacles with both direct and template-based approaches.

Background

The motivation behind this conversion stems from the implementation of currying in C via variadic templates. However, this technique becomes problematic when attempting to pass a lambda as an argument to a variadic function.

Limitations of Template Type Deduction

The primary challenge lies in the inability of template type deduction to deduce the correct template argument for std::function based solely on the lambda expression. This is because template type deduction does not consider type conversions.

Solution Using Identity Wrappers

One workaround involves wrapping the lambda argument within an identity type. This allows the compiler to ignore the lambda's dependency during type deduction. However, this approach requires additional parameters, which may not align with the desired use case.

Current Limitations

In situations where explicit template parameter specification is undesirable and no other deductible arguments are available, it becomes impossible for the compiler to deduce the desired std::function template type. This limitation prevents the direct conversion of lambdas into std::function objects without explicit parameter specification or additional arguments.

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