From: Gustavo Niemeyer Date: Mon, 15 Aug 2011 03:56:01 +0000 (-0300) Subject: exp/template: support field syntax on maps X-Git-Tag: weekly.2011-08-17~52 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=e3df71f50bfd7e2d0706a6fa8d3ff56b3d7c4b0a;p=gostls13.git exp/template: support field syntax on maps While using exp/template in practice, the syntax for indexing values using the "index" action was found to be very inconvenient for frequent use when handling dynamic data from maps such as the ones used with json and yaml, that use a type like map[string]interface{}. For these kinds of maps, the default handling of fields as {{.Field}} makes the task of handling the several references significantly more pleasant and elegant, and is equivalent to what's currently done in the "template" package and in other external packages (e.g. mustache). Even with this change, the index action is still relevant as it allows indexing maps in other scenarios where keys wouldn't be valid field names. R=golang-dev, r, gustavo CC=golang-dev https://golang.org/cl/4898043 --- diff --git a/src/pkg/exp/template/doc.go b/src/pkg/exp/template/doc.go index 46a38040e3..f65946aed9 100644 --- a/src/pkg/exp/template/doc.go +++ b/src/pkg/exp/template/doc.go @@ -101,6 +101,17 @@ An argument is a simple value, denoted by one of the following. .Field1.Field2 Fields can also be evaluated on variables, including chaining: $x.Field1.Field2 + - The name of a key of the data, which must be a map, preceded + by a period, such as + .Key + The result is the map element value indexed by the key. + Key invocations may be chained and combined with fields to any + depth: + .Field1.Key1.Field2.Key2 + Although the key must be an alphanumeric identifier, unlike with + field names they do not need to start with an upper case letter. + Keys can also be evaluated on variables, including chaining: + $x.key1.key2 - The name of a niladic method of the data, preceded by a period, such as .Method @@ -109,9 +120,9 @@ An argument is a simple value, denoted by one of the following. any type) or two return values, the second of which is an os.Error. If it has two and the returned error is non-nil, execution terminates and an error is returned to the caller as the value of Execute. - Method invocations may be chained and combined with fields + Method invocations may be chained and combined with fields and keys to any depth: - .Field1.Method1.Field2.Method2 + .Field1.Key1.Method1.Field2.Key2.Method2 Methods can also be evaluated on variables, including chaining: $x.Method1.Field - The name of a niladic function, such as diff --git a/src/pkg/exp/template/exec.go b/src/pkg/exp/template/exec.go index 06e5d2b3b8..08cb390900 100644 --- a/src/pkg/exp/template/exec.go +++ b/src/pkg/exp/template/exec.go @@ -394,13 +394,14 @@ func (s *state) evalField(dot reflect.Value, fieldName string, args []parse.Node if method, ok := methodByName(ptr, fieldName); ok { return s.evalCall(dot, method, fieldName, args, final) } + hasArgs := len(args) > 1 || final.IsValid() // It's not a method; is it a field of a struct? receiver, isNil := indirect(receiver) if receiver.Kind() == reflect.Struct { tField, ok := receiver.Type().FieldByName(fieldName) if ok { field := receiver.FieldByIndex(tField.Index) - if len(args) > 1 || final.IsValid() { + if hasArgs { s.errorf("%s is not a method but has arguments", fieldName) } if tField.PkgPath == "" { // field is exported @@ -408,6 +409,16 @@ func (s *state) evalField(dot reflect.Value, fieldName string, args []parse.Node } } } + // If it's a map, attempt to use the field name as a key. + if receiver.Kind() == reflect.Map { + nameVal := reflect.ValueOf(fieldName) + if nameVal.Type().AssignableTo(receiver.Type().Key()) { + if hasArgs { + s.errorf("%s is not a method but has arguments", fieldName) + } + return receiver.MapIndex(nameVal) + } + } if isNil { s.errorf("nil pointer evaluating %s.%s", typ, fieldName) } diff --git a/src/pkg/exp/template/exec_test.go b/src/pkg/exp/template/exec_test.go index 8a610da63b..82f56e13cb 100644 --- a/src/pkg/exp/template/exec_test.go +++ b/src/pkg/exp/template/exec_test.go @@ -39,6 +39,8 @@ type T struct { MSI map[string]int MSIone map[string]int // one element, for deterministic output MSIEmpty map[string]int + MXI map[interface{}]int + MII map[int]int SMSI []map[string]int // Empty interfaces; used to see if we can dig inside one. Empty0 interface{} // nil @@ -85,6 +87,8 @@ var tVal = &T{ SB: []bool{true, false}, MSI: map[string]int{"one": 1, "two": 2, "three": 3}, MSIone: map[string]int{"one": 1}, + MXI: map[interface{}]int{"one": 1}, + MII: map[int]int{1: 1}, SMSI: []map[string]int{ {"one": 1, "two": 2}, {"eleven": 11, "twelve": 12}, @@ -211,6 +215,14 @@ var execTests = []execTest{ {".X", "-{{.X}}-", "-x-", tVal, true}, {".U.V", "-{{.U.V}}-", "-v-", tVal, true}, + // Fields on maps. + {"map .one", "{{.MSI.one}}", "1", tVal, true}, + {"map .two", "{{.MSI.two}}", "2", tVal, true}, + {"map .NO", "{{.MSI.NO}}", "", tVal, true}, + {"map .one interface", "{{.MXI.one}}", "1", tVal, true}, + {"map .WRONG args", "{{.MSI.one 1}}", "", tVal, false}, + {"map .WRONG type", "{{.MII.one}}", "", tVal, false}, + // Dots of all kinds to test basic evaluation. {"dot int", "<{{.}}>", "<13>", 13, true}, {"dot uint", "<{{.}}>", "<14>", uint(14), true},