In C#, const, readonly, and static readonly are all used to define constants or values that cannot be changed after they are assigned a value. However, they have different behaviors and use cases. Let’s delve into each of them:
const:
- Constants declared with the const keyword are implicitly static. They are evaluated at compile time and their values must be known at compile time.
- Constants are always implicitly static and readonly, meaning they cannot be modified after their initial assignment.
- Constants are typically used for values that won’t change and can be computed at compile time, like mathematical constants.
readonly:
- readonly fields are evaluated at runtime, which means their values can be determined and assigned in the constructor or through inline initialization.
- readonly fields can have different values for different instances of the class, whereas const fields are shared across all instances.
- readonly fields can be assigned in the constructor or directly when declared, but not elsewhere in the code.
Static readonly:
- Static readonly fields are shared across all instances of the class, and their values are evaluated at runtime.
- These fields can be assigned in the constructor or through inline initialization, but only once and usually within a static constructor.
When to Use Each:
- Use const for values that are known at compile time and won’t change, like mathematical constants.
- Use readonly for instance-specific values that are determined at runtime but won’t change after initialization.
- Use static readonlyfor values that are shared across instances and won’t change after initialization.
Remember that the choice of which to use depends on the requirements of your code and the nature of the constant values you’re defining.