Initialization Lists vs. Assignments in Constructors: When Should You Use Which?

In-Depth Analysis of Initialization Techniques in Constructors

Consider the following code:

MyClass::MyClass() : _capacity(15), _data(NULL), _len(0) {}

Versus:

MyClass::MyClass() { _capacity = 15; _data = NULL; _len = 0; }

It's important to note that the choice between using an initialization list and assigning values in a constructor depends on the specific requirements of member initialization.

Member Initialization List

An initialization list is used to initialize all members of the current object upon its construction. It is typically recommended for several scenarios:

1. Initializing Constant Members: Constant members must be initialized in the initialization list, as they cannot be modified after construction.
2. Initializing References: References must also be initialized in the initialization list, as they cannot be assigned values after construction.
3. Passing Parameters to Base Class Constructors: If the base class requires parameters for its constructor, these parameters must be passed through the initialization list.

In the example provided, where _capacity, _data, and _len are not constant members or references, both approaches are valid and will result in equivalent internally generated code. However, if any of these members were constant or a reference, the initialization list would be required.

Regular Assignments vs. Initialization List

While regular assignments within the constructor are generally considered acceptable for non-constant member variables, they have some drawbacks:

• Increased code length and complexity.
• Potential for errors, such as assigning values to constant members or attempting to initialize references.
• Reduced readability and developer predictability.

Conclusion

The use of an initialization list is recommended for initializing constant members, references, and passing parameters to base class constructors. For regular member variables, regular assignment statements may be more suitable, but the initialization list still provides a more concise and accurate approach.

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