Function Parameters: Summary

Summary #

• A parameter is what the function takes from its calling function to accomplish its task.

• An argument is an expression (e.g. a variable) that is passed to a function as a parameter from the calling function.

• Every argument is passed by copy.

  • However, for reference types, it is the reference that is copied, not the original variable.

• in specifies that the parameter is used only for data input.

• out specifies that the parameter is used only for data output.

• ref specifies that the parameter is used for data input and data output.

• auto ref is used in templates only. It specifies that if the argument is an lvalue, then a reference to it is passed; if the argument is an rvalue, then it is passed by copy.

• const guarantees that the parameter is not modified inside the function.

  • Remember that const is transitive: any data reached through a const variable is const as well.

• immutable requires the argument to be immutable.

• inout appears both at the parameter and the return type and transfers the mutability of the parameter to the return type.

• lazy is used to make a parameter be evaluated when (and every time) it is actually used.

• scope guarantees that no reference to the parameter will be leaked from the function.

• shared requires the parameter to be shared.

• return on a parameter requires the parameter to live longer than the returned reference.

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In the next lesson, you will find a coding challenge related to function parameters.