go-tagexpr

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

Status

In development

Example

type T struct {
	A int              `tagexpr:"$<0||$>=100"`
	B string           `tagexpr:"len($)>1 || regexp('^\\w*$')"`
	C bool             `tagexpr:"{expr1:(G)$['J']>0 && $}{expr2:'C must be true when T.G.J>0'}"`
	D []string         `tagexpr:"{expr1:len($)>0 && $[0]=='D'} {expr2:sprintf('Invalid D:%s',$)}"`
	E map[string]int   `tagexpr:"{expr1:$k!='' && $v>0}{expr2:$['E']>0}"`
	F map[string][]int `tagexpr:"$$v>0 && len($['F'])>0 && $['F'][0]>1"`
	G struct{ J int }
}

Syntax

Struct tag syntax spec:

type T struct {
    Field1 T1 `tagName:"expression"`
    Field2 T2 `tagName:"{exprName:expression} [{exprName2:expression2}]..."`
    ...
}

NOTE: The exprName under the same struct field cannot be the same！

Operator or Expression example	Explain
true	bool "true"
false	bool "false"
1	float64 "1"
1.0	float64 "1.0"
'S'	String "S"
+	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
$	Shorthand for (X)$, omit (X) to indicate current struct field value
(X)$['A']	Map or struct field value with name A in the struct field X
(X)$[0]	The 0th element of the struct field X(type: map, slice, array)
(X)$$	Traverse each element of the struct field X(type: map, slice, array)
(X)$k	Traverse each element key of the struct field X(type: map, slice, array)
(X)$v	Traverse each element value of the struct field X(type: map, slice, array)
len((X)$)	Built-in function len, the length of struct field X
len()	Built-in function len, the length of the current struct field
regexp('^\\w*$', (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 string float64
• * / %
• + -
• < <= > >=
• == !=
• &&
• ||