Why Can't I Define a Default Constructor for a .NET Struct?

Why are explicit default constructors prohibited for .NET structs?

In the .NET framework, value types (structs) are not permitted to have user-defined parameterless constructors. This restriction is imposed by the Common Language Infrastructure (CLI) specification. The compiler automatically generates a default constructor that initializes all members to their default values (zero or null).

The Rationale Behind the Restriction

This restriction is primarily driven by performance optimization. When creating arrays or collections of structs, the Common Language Runtime (CLR) employs highly efficient memory allocation and zeroing techniques. Requiring the execution of a user-defined constructor for each element would drastically reduce this efficiency.

Constructor Behavior

It's important to note that the default constructor (whether compiler-generated or user-defined) isn't always invoked. It's bypassed when creating arrays or declaring uninitialized struct instances.

Workarounds

To assign specific default values to a struct's members, utilize a constructor with parameters. If performance is paramount, consider using lists instead of arrays to avoid unnecessary constructor calls during initialization.

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