coerce

Overview ¶

Package coerce provides loose type coercion and assignment into native Go types.

Primitive Types ¶

This package considers the following types to be primitive types:

bool
float32 float64
int8 int16 int32 int64 int
uint8 uint16 uint32 uint64 uint
string

Coercion Logic ¶

All coercion functions use the same basic logic to coerce an incoming value v:

for {
	v is primitive
		return coerced value or error
	v's underlying kind is primitive
		// convert v to underlying kind and try again
		v = UnderlyingKind(v); continue
	v is a pointer
		// dereference v and try again
		v = *v; continue
	v is a slice
		// try again with last slice element
		v = v[len(v)-1]; continue
	ErrUnsupported
}

If v is a primitive type it will be coerced via type coercion, one or more calls to the strconv package, or a small amount of custom logic.

If v's underlying kind is primitive it is converted to the underlying primitive and the loop restarts with a continue statement.

If v is a pointer or any pointer chain it is followed until the final value and the loop restarts with a continue statement. A nil pointer shortcuts and returns an appropriate zero value.

If v is a slice then v is reassigned to the last element and the loop starts again with a continue statement. An empty slice shortcuts and returns an appropriate zero value.

All other types for v (e.g. chan, map, func, etc) return a zero value and ErrUnsupported.

Overflow ¶

During numeric coercions this package checks incoming values against the minimum and maximum value for the target type. If the incoming value is out of range for the target type ErrOverflow is returned.

Otherwise the coercion is made with type conversion.

String Parsing ¶

Where necessary this package will call into strconv to parse values for bool, int, float, or uint.

If a call to strconv returns error this package will return the zero value for the target type and either ErrOverflow or ErrInvalid depending on the error received from strconv.

This package may make multiple calls to strconv to parse an incoming string. For example it may first try strconv.ParseInt, followed by strconv.ParseUint, and finally strconv.ParseFloat to parse a string. If any of the calls succeed then type coercion continues with the parsed value.