How Does Go Handle Memory When Using Alias Types and Passing Values to Functions?

Aliasing and Copying in Go

When working with custom types in Go, it's crucial to understand the behavior of alias type conversions regarding memory management.

Alias Type Conversions

An alias type is a new type that references the underlying type of an existing type. For instance, the following code creates an alias type MyString for string:

type MyString string

Variables of the alias type refer to the same memory location as the underlying type. Thus, converting a value between the alias type and underlying type doesn't create a copy.

Example

Consider the following code:

type MyString string
var s = "very long string"
var ms = MyString(s)
var s2 = string(s)

In this example, ms and s2 are not full copies of s. Instead, they are simply string struct copies referencing the same memory location.

Function Passing

When passing a value to a function, Go creates a copy by default. However, for slices and strings, which are immutable, only the descriptor (a small struct) is copied. The underlying data remains in the same memory location.

The following function call:

func foo(s MyString) {
  ...
}
foo(ms(s))

does not copy the entire string. It only creates a copy of the MyString descriptor, which references the original string data.

Conclusion

Understanding alias type conversions and the memory management behavior when passing values to functions is crucial for efficient Go programming. Alias type conversions themselves do not create copies, but function passing does (except for immutable types like strings and slices).

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