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Example:
type MyString string
var s = "very long string"
var ms = MyString(s)
var s2 = string(s)
Are ms or s2 a full copy of s (as it would be done with []byte(s))? Or they are just a string struct copies (which keeps the real value in a pointer)?
What if we are passing this to a function? E.g.:
func foo(s MyString){
...
}
foo(ms(s)) // do we copy s here?
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Type conversion is a way to convert a variable from one data type to another data type. For example, if you want to store a long value into a simple integer then you can type cast long to int. You can convert values from one type to another using the cast operator. Its syntax is as follows − type_name(expression)
Still, the Go language is different, as it doesn't support an Automatic Type Conversion or Implicit Type Conversion even if the data types are compatible.
It provides several built-in types such as string, bool, int and float64. Go supports composite types such as array, slice, map and channel. Composite types are made up of other types – built-in types and user-defined types.
In Go, we can define new types by using the following form. In the syntax, type is a keyword.
Spec: Conversions:
Specific rules apply to (non-constant) conversions between numeric types or to and from a string type. These conversions may change the representation of
xand incur a run-time cost. All other conversions only change the type but not the representation ofx.
So converting to and from the underlying type of your custom type does not make a copy of it.
When you pass a value to a function or method, a copy is made and passed. If you pass a string to a function, only the structure describing the string will be copied and passed, since strings are immutable.
Same is true if you pass a slice (slices are also descriptors). Passing a slice will make a copy of the slice descriptor but it will refer to the same underlying array.
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