Remove "magical" NewPrefix function, rename Prefix to Encoder.

encoder.go

@@ -0,0 +1,53 @@
+package multibase
+
+import (
+	"fmt"
+)
+
+// Encoder is a multibase encoding that is verified to be supported and
+// supports an Encode method that does not return an error
+type Encoder struct {
+	enc Encoding
+}
+
+// NewEncoder create a new Encoder from an Encoding
+func NewEncoder(base Encoding) (Encoder, error) {
+	_, ok := EncodingToStr[base]
+	if !ok {
+		return Encoder{-1}, fmt.Errorf("Unsupported multibase encoding: %d", base)
+	}
+	return Encoder{base}, nil
+}
+
+// EncoderByName creates an encoder from a string, the string can
+// either be the multibase name or single character multibase prefix
+func EncoderByName(str string) (Encoder, error) {
+	var base Encoding
+	ok := true
+	if len(str) == 0 {
+		return Encoder{-1}, fmt.Errorf("Empty multibase encoding")
+	} else if len(str) == 1 {
+		base = Encoding(str[0])
+		_, ok = EncodingToStr[base]
+	} else {
+		base, ok = Encodings[str]
+	}
+	if !ok {
+		return Encoder{-1}, fmt.Errorf("Unsupported multibase encoding: %s", str)
+	}
+	return Encoder{base}, nil
+}
+
+func (p Encoder) Encoding() Encoding {
+	return p.enc
+}
+
+// Encode encodes the multibase using the given Encoder.
+func (p Encoder) Encode(data []byte) string {
+	str, err := Encode(p.enc, data)
+	if err != nil {
+		// should not happen
+		panic(err)
+	}
+	return str
+}