github.com/kolbycrouch/elvish@v0.14.1-0.20210614162631-215b9ac1c423/pkg/eval/vals/string.go (about)

     1  package vals
     2  
     3  import (
     4  	"math"
     5  	"strconv"
     6  	"strings"
     7  )
     8  
     9  // Stringer wraps the String method.
    10  type Stringer interface {
    11  	// Stringer converts the receiver to a string.
    12  	String() string
    13  }
    14  
    15  // ToString converts a Value to string. It is implemented for the builtin
    16  // float64 and string types, and type satisfying the Stringer interface. It
    17  // falls back to Repr(v, NoPretty).
    18  func ToString(v interface{}) string {
    19  	switch v := v.(type) {
    20  	case int:
    21  		return strconv.Itoa(v)
    22  	case float64:
    23  		return formatFloat64(v)
    24  	case string:
    25  		return v
    26  	case Stringer:
    27  		return v.String()
    28  	default:
    29  		return Repr(v, NoPretty)
    30  	}
    31  }
    32  
    33  func formatFloat64(f float64) string {
    34  	// Go's 'g' format is not quite ideal for printing floating point numbers;
    35  	// it uses scientific notation too aggressively, and relatively small
    36  	// numbers like 1234567 are printed with scientific notations, something we
    37  	// don't really want.
    38  	//
    39  	// So we use a different algorithm for determining when to use scientific
    40  	// notation. The algorithm is reverse-engineered from Racket's; it may not
    41  	// be a perfect clone but hopefully good enough.
    42  	//
    43  	// See also b.elv.sh/811 for more context.
    44  	s := strconv.FormatFloat(f, 'f', -1, 64)
    45  	noPoint := !strings.ContainsRune(s, '.')
    46  	if (noPoint && len(s) > 14 && s[len(s)-1] == '0') ||
    47  		strings.HasPrefix(s, "0.0000") {
    48  		return strconv.FormatFloat(f, 'e', -1, 64)
    49  	} else if noPoint && !math.IsNaN(f) && !math.IsInf(f, 0) {
    50  		return s + ".0"
    51  	}
    52  	return s
    53  }