


Why Can't C Template Parameters Be Inferred for Class Constructors Like Function Templates?
Dec 08, 2024 pm 05:44 PMClass Constructor Template Inference Controversy
Template parameters can be conveniently inferred from function arguments, as in the following code:
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However, a similar approach is not allowed for class constructors, which has raised questions among C programmers. Why not?
The reason behind this inconsistency lies in the complexities of object construction. Constructors are not the only entry point for a class. Copy constructors and assignment operators also play vital roles, and inferring template parameters from only the constructor could lead to ambiguities.
Consider the following example:
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If template inference were allowed, the following code would be valid:
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But what if we used copy construction or assignment operators?
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In this case, it would be challenging for the compiler to determine the template type of MyClass pm.
To alleviate this issue, C 17 introduced type deduction from constructor arguments. This allows template parameters to be inferred from constructor parameters, eliminating the need for explicit type arguments in certain situations. For example:
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It's important to note that this inference feature is still under development and may be subject to modifications in future C standards. Nevertheless, it marks a significant step towards simplifying code and improving type safety.
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