An interesting go struct tag expression syntax for field validation, etc.
-
Validator: A powerful validator that supports struct tag expression
-
Binding: A powerful HTTP request parameters binder that supports struct tag expression
- 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
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:"$"`
}
}
vm := tagexpr.New("tagexpr")
t := &T{
A: 107,
B: "abc",
C: true,
d: []string{"x", "y"},
e: map[string]int{"len": 1},
e2: map[string]*int{"len": new(int)},
f: struct {
g int `tagexpr:"$"`
}{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
}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 |
Operator priority(high -> low):
()!boolfloat64stringnil*/%+-<<=>>===!=&&||
field_lv1.field_lv2...field_lvn
- 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
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