stringfrom

stringfrom

Convert pointers and other values to strings for display, with a chosen text for nil. Use it to render optional fields in templates, CSV files or log messages without writing a nil check for every field.

import "github.com/domonda/go-types/strutil/stringfrom"

Pointer functions

Every *Ptr function takes a pointer and optional strForNil ...string arguments. For a nil pointer it returns the strForNil arguments joined without a separator, so Ptr(nil) is "", Ptr(nil, "n/a") is "n/a" and Ptr(nil, "<", "nil", ">") is "<nil>".

Function	Non-nil result	Returns strForNil for
Ptr(ptr *string, strForNil ...string) string	*ptr	nil
TimePtr(ptr *time.Time, strForNil ...string) string	ptr.String(), like "2024-03-01 12:30:00 +0000 UTC"	nil and a pointer to the zero time
UUIDPtr(ptr *uu.ID, strForNil ...string) string	ptr.String(), the canonical UUID form	nil only, a pointer to uu.IDNil gives "00000000-0000-0000-0000-000000000000"
IntPtr(ptr *int, strForNil ...string) string	decimal, like "-3"	nil
UintPtr(ptr *uint, strForNil ...string) string	decimal, like "7"	nil
Int64Ptr(ptr *int64, strForNil ...string) string	decimal	nil
Float64Ptr(ptr *float64, strForNil ...string) string	strconv.FormatFloat(*ptr, 'f', -1, 64): no exponent, like "0.1" or "1000000000000000000000" for 1e21; "NaN", "+Inf", "-Inf"	nil
BoolPtr(ptr *bool, strForNil ...string) string	"true" or "false"	nil

Other functions

Function	Description
Bool(boolVal bool, trueString, falseString string) string	trueString if boolVal is true, else falseString.
Interface(i any) string	Converts i, or the value i points to: a value with a Format, Error or String method, also one with a pointer receiver, with that method, a value of string kind as is, any other value with fmt.Sprint. A non-pointer value gives the same string as a pointer to it. Returns "" for nil, a nil pointer, and a nil map, slice, func, channel or interface value.

None of the functions panics for nil input.

Gotchas

• TimePtr uses time.Time.String, which is not RFC 3339 and includes the monotonic clock reading for times from time.Now(), like "2026-10-12 14:15:32.261641 +0200 CEST m=+0.000682459". Call Round(0) on the time or format it yourself if you need a stable layout.
• UUIDPtr does not treat uu.IDNil as nil, unlike TimePtr with the zero time.
• Interface dereferences only one level: a pointer to a non-nil pointer prints as an address.

Example

package main

import (
	"fmt"
	"time"

	"github.com/domonda/go-types/strutil/stringfrom"
	"github.com/domonda/go-types/uu"
)

func main() {
	var name *string
	fmt.Println(stringfrom.Ptr(name, "<unknown>"))

	paid := time.Date(2024, 3, 1, 12, 30, 0, 0, time.UTC)
	var zero time.Time
	fmt.Println(stringfrom.TimePtr(&paid, "unpaid"))
	fmt.Println(stringfrom.TimePtr(&zero, "unpaid"))

	fmt.Println(stringfrom.UUIDPtr(nil, "no ID"))
	fmt.Println(stringfrom.UUIDPtr(&uu.IDNil, "no ID"))

	amount := 1234.5
	fmt.Println(stringfrom.Float64Ptr(&amount))
	fmt.Println(stringfrom.Bool(true, "yes", "no"))

	n := 42
	fmt.Printf("%q %q %q\n", stringfrom.Interface(&n), stringfrom.Interface(n), stringfrom.Interface(nil))
	// Output:
	// <unknown>
	// 2024-03-01 12:30:00 +0000 UTC
	// unpaid
	// no ID
	// 00000000-0000-0000-0000-000000000000
	// 1234.5
	// yes
	// "42" "42" ""
}

Related

• strutil: string helpers of the parent package, including DerefPtr and StringToPtrEmptyToNil for *string.
• Root package reference: types.FromPtr and types.FromPtrOr for pointers of any type. Go 1.26's new(expr) replaces the removed Ptr functions.
• uu: the uu.ID type formatted by UUIDPtr.
• nullable: optional values as types instead of pointers.
• How to store optional values