go-tagexpr

An interesting go struct tag expression syntax for field validation, etc.

Usage

• Validator: A powerful validator that supports struct tag expression

• Binding: A powerful HTTP request parameters binder that supports struct tag expression

Feature

• Support for a variety of common operator
• Support for accessing arrays, slices, members of the dictionary
• Support access to any field in the current structure
• Support access to nested fields, non-exported fields, etc.
• Support registers function expression
• Built-in len, sprintf, regexp functions
• Support single mode and multiple mode to define expression
• Parameter check subpackage
• Use offset pointers to directly take values, better performance
• Required go version ≥1.9

Example

package tagexpr_test

import (
	"fmt"

	tagexpr "github.com/bytedance/go-tagexpr"
)

func Example() {
	type T struct {
		A  int             `tagexpr:"$<0, $>=100"`
		B  string          `tagexpr:"len($)>1 && regexp('^\\w*$')"`
		C  bool            `tagexpr:"expr1:(f.g)$>0 && $; expr2:'C must be true when T.f.g>0'"`
		d  []string        `tagexpr:"@:len($)>0 && $[0]=='D'; msg:sprintf('invalid d: %v',$)"`
		e  map[string]int  `tagexpr:"len($)==$['len']"`
		e2 map[string]*int `tagexpr:"len($)==$['len']"`
		f  struct {
			g int `tagexpr:"$"`
		}
	}

	vm := tagexpr.New("tagexpr")
	t := &T{
		A:  107,
		B:  "abc",
		C:  true,
		d:  []string{"x", "y"},
		e:  map[string]int{"len": 1},
		e2: map[string]*int{"len": new(int)},
		f: struct {
			g int `tagexpr:"$"`
		}{1},
	}

	tagExpr, err := vm.Run(t)
	if err != nil {
		panic(err)
	}

	fmt.Println(tagExpr.Eval("A"))
	fmt.Println(tagExpr.Eval("B"))
	fmt.Println(tagExpr.Eval("C@expr1"))
	fmt.Println(tagExpr.Eval("C@expr2"))
	if !tagExpr.Eval("d").(bool) {
		fmt.Println(tagExpr.Eval("d@msg"))
	}
	fmt.Println(tagExpr.Eval("e"))
	fmt.Println(tagExpr.Eval("e2"))
	fmt.Println(tagExpr.Eval("f.g"))

	// Output:
	// true
	// true
	// true
	// C must be true when T.f.g>0
	// invalid d: [x y]
	// true
	// false
	// 1
}

Syntax

Struct tag syntax spec:

type T struct {
	// Single model
    Field1 T1 `tagName:"expression"`
	// Multiple model
    Field2 T2 `tagName:"exprName:expression; [exprName2:expression2;]..."`
	// Omit it
    Field3 T3 `tagName:"-"`
    // Omit it when it is nil
    Field4 T4 `tagName:"?"`
    ...
}

NOTE: The exprName under the same struct field cannot be the same！, Operator or Operand, Explain, -----, ---------, true false, boolean, 0 0.0, float64 "0", '', String, \\', Escape ' delims in string, \", Escape " delims in string, nil, nil, undefined, !, not, suitable for bool, string, float64, nil, $ and (), +, Digital addition or string splicing, -, Digital subtraction or negative, *, Digital multiplication, /, Digital division, %, division remainder, as: float64(int64(a)%int64(b)), ==, eq, !=, ne, >, gt, >=, ge, <, lt, <=, le, &&, Logic and, \, \, , Logic or, (), Expression group, (X)$, Struct field value named X, (X.Y)$, Struct field value named X.Y, $, Shorthand for (X)$, omit (X) to indicate current struct field value, (X)$['A'], Map value with key A or struct A sub-field in the struct field X, (X)$[0], The 0th element or sub-field of the struct field X(type: map, slice, array, struct), len((X)$), Built-in function len, the length of struct field X, regexp('^\\w*$', (X)$), Regular match the struct field X, return boolean, regexp('^\\w*$'), Regular match the current struct field, return boolean, sprintf('X value: %v', (X)$), fmt.Sprintf, format the value of struct field X,

Operator priority(high -> low):

• () ! bool float64 string nil
• * / %
• + -
• < <= > >=
• == !=
• &&
• ,

Field Selector

field_lv1.field_lv2...field_lvn

Expression Selector

• If expression is single model or exprName is @:

field_lv1.field_lv2...field_lvn

• If expression is multiple model and exprName is not @:

field_lv1.field_lv2...field_lvn@exprName

Benchmark

goos: darwin
goarch: amd64
pkg: github.com/bytedance/go-tagexpr
BenchmarkTagExpr-4   	10000000	       148 ns/op	      32 B/op	       3 allocs/op
BenchmarkReflect-4   	10000000	       182 ns/op	      16 B/op	       2 allocs/op
PASS

Go to test code