116 lines
3.4 KiB
Go
116 lines
3.4 KiB
Go
// Copyright (c) 2019 Uber Technologies, Inc.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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// THE SOFTWARE.
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package fx
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import (
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"fmt"
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"reflect"
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)
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// Populate sets targets with values from the dependency injection container
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// during application initialization. All targets must be pointers to the
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// values that must be populated. Pointers to structs that embed In are
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// supported, which can be used to populate multiple values in a struct.
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//
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// Annotating each pointer with ParamTags is also supported as a shorthand
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// to passing a pointer to a struct that embeds In with field tags. For example:
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//
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// var a A
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// var b B
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// fx.Populate(
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// fx.Annotate(
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// &a,
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// fx.ParamTags(`name:"A"`)
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// ),
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// fx.Annotate(
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// &b,
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// fx.ParamTags(`name:"B"`)
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// )
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// )
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//
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// Code above is equivalent to the following:
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//
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// type Target struct {
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// fx.In
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//
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// a A `name:"A"`
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// b B `name:"B"`
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// }
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// var target Target
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// ...
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// fx.Populate(&target)
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//
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// This is most helpful in unit tests: it lets tests leverage Fx's automatic
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// constructor wiring to build a few structs, but then extract those structs
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// for further testing.
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func Populate(targets ...interface{}) Option {
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// Validate all targets are non-nil pointers.
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fields := make([]reflect.StructField, len(targets)+1)
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fields[0] = reflect.StructField{
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Name: "In",
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Type: reflect.TypeOf(In{}),
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Anonymous: true,
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}
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for i, t := range targets {
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if t == nil {
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return Error(fmt.Errorf("failed to Populate: target %v is nil", i+1))
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}
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var (
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rt reflect.Type
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tag reflect.StructTag
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)
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switch t := t.(type) {
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case annotated:
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rt = reflect.TypeOf(t.Target)
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tag = reflect.StructTag(t.ParamTags[0])
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targets[i] = t.Target
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default:
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rt = reflect.TypeOf(t)
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}
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if rt.Kind() != reflect.Ptr {
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return Error(fmt.Errorf("failed to Populate: target %v is not a pointer type, got %T", i+1, t))
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}
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fields[i+1] = reflect.StructField{
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Name: fmt.Sprintf("Field%d", i),
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Type: rt.Elem(),
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Tag: tag,
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}
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}
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// Build a function that looks like:
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//
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// func(t1 T1, t2 T2, ...) {
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// *targets[0] = t1
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// *targets[1] = t2
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// [...]
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// }
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//
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fnType := reflect.FuncOf([]reflect.Type{reflect.StructOf(fields)}, nil, false /* variadic */)
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fn := reflect.MakeFunc(fnType, func(args []reflect.Value) []reflect.Value {
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arg := args[0]
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for i, target := range targets {
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reflect.ValueOf(target).Elem().Set(arg.Field(i + 1))
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}
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return nil
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})
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return Invoke(fn.Interface())
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}
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