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https://github.com/bytedance/go-tagexpr

An interesting go struct tag expression syntax for field validation, etc.
https://github.com/bytedance/go-tagexpr

binding dsl expression go struct-tag validator

Last synced: 26 days ago
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An interesting go struct tag expression syntax for field validation, etc.

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# go-tagexpr [![report card](https://goreportcard.com/badge/github.com/bytedance/go-tagexpr?style=flat-square)](http://goreportcard.com/report/bytedance/go-tagexpr) [![GoDoc](https://img.shields.io/badge/godoc-reference-blue.svg?style=flat-square)](http://godoc.org/github.com/bytedance/go-tagexpr)



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



## Usage



- **[Validator](https://github.com/bytedance/go-tagexpr/tree/master/validator)**: A powerful validator that supports struct tag expression



- **[Binding](https://github.com/bytedance/go-tagexpr/tree/master/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 variable

- 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



```go

package tagexpr_test



import (

	"fmt"



	tagexpr "github.com/bytedance/go-tagexpr/v2"

)



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:"$"`

		}

		h  int 				`tagexpr:"$>minVal"`

	}



	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},

		h: 10,

	}



	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"))

	fmt.Println(tagExpr.EvalWithEnv("h", map[string]interface{}{"minVal": 9}))

	fmt.Println(tagExpr.EvalWithEnv("h", map[string]interface{}{"minVal": 11}))



	// Output:

	// true

	// true

	// true

	// C must be true when T.f.g>0

	// invalid d: [x y]

	// true

	// false

	// 1

	// true

	// false

}

```



## 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|

|`+`|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|

|`mblen((X)$)`|the length of string field X (character number)|

|`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|

|`range(KvExpr, forEachExpr)`|Iterate over an array, slice, or dictionary 
 - `#k` is the element key var 
 - `#v` is the element value var 
 - `##` is the number of elements 
 - e.g. [example](spec_range_test.go)|

|`in((X)$, enum_1, ...enum_n)`|Check if the first parameter is one of the enumerated parameters|



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](https://github.com/bytedance/go-tagexpr/blob/master/tagexpr_test.go#L9-L56)