Cast/convert int to rune in Go

Question

Assuming I have an int64 variable (or other integer size) representing a valid unicode code-point, and I want to convert it into a rune in Go, what do I do?

In C I would have used a type cast something like:

c = (char) i;  // 7 bit ascii only

But in Go, a type assertion won't work:

c, err = rune.( i)

Suggestions?

Answer 1

You just want rune(i). Casting is done via type(x).

Type assertions are something different. You use a type assertion when you need to go from a less specific type (like interface{}) to a more specific one. Additionally, a cast is checked at compile time, where type assertions happen at runtime.

Here's how you use a type assertion:

var (
    x interface{}
    y int
    z string
)
x = 3

// x is now essentially boxed. Its type is interface{}, but it contains an int.
// This is somewhat analogous to the Object type in other languages
// (though not exactly).

y = x.(int)    // succeeds
z = x.(string) // compiles, but fails at runtime 

Answer 2

In Go, you want to do a conversion.

Conversions

Conversions are expressions of the form T(x) where T is a type and x is an expression that can be converted to type T.

Conversion = Type "(" Expression ")" .

A non-constant value x can be converted to type T in any of these cases:

• x is assignable to T.
• x's type and T have identical underlying types.
• x's type and T are unnamed pointer types and their pointer base types have identical underlying types.
• x's type and T are both integer or floating point types.
• x's type and T are both complex types.
• x is an integer or has type []byte or []rune and T is a string type.
• x is a string and T is []byte or []rune.

You want to convert x, of type int, int32, or int64, to T of type rune, an alias for type int32. x's type and T are both integer types.

Therefore, T(x) is allowed and is written rune(x), for your example, c = rune(i).