hub.fastgit.org/hashicorp/consul.git@v1.4.5/agent/config/merge.go (about)

     1  package config
     2  
     3  import (
     4  	"fmt"
     5  	"reflect"
     6  )
     7  
     8  // Merge recursively combines a set of config file structures into a single structure
     9  // according to the following rules:
    10  //
    11  // * only values of type struct, slice, map and pointer to simple types are allowed. Other types panic.
    12  // * when merging two structs the result is the recursive merge of all fields according to the rules below
    13  // * when merging two slices the result is the second slice appended to the first
    14  // * when merging two maps the result is the second map overlaid on the first
    15  // * when merging two pointer values the result is the second value if it is not nil, otherwise the first
    16  func Merge(files ...Config) Config {
    17  	var a Config
    18  	for _, b := range files {
    19  		a = merge(a, b).(Config)
    20  	}
    21  	return a
    22  }
    23  
    24  func merge(a, b interface{}) interface{} {
    25  	return mergeValue(reflect.ValueOf(a), reflect.ValueOf(b)).Interface()
    26  }
    27  
    28  func mergeValue(a, b reflect.Value) reflect.Value {
    29  	switch a.Kind() {
    30  	case reflect.Map:
    31  		r := reflect.MakeMap(a.Type())
    32  		for _, k := range a.MapKeys() {
    33  			v := a.MapIndex(k)
    34  			r.SetMapIndex(k, v)
    35  		}
    36  		for _, k := range b.MapKeys() {
    37  			v := b.MapIndex(k)
    38  			r.SetMapIndex(k, v)
    39  		}
    40  		return r
    41  
    42  	case reflect.Ptr:
    43  		if !b.IsNil() {
    44  			return b
    45  		}
    46  		return a
    47  
    48  	case reflect.Slice:
    49  		if !a.IsValid() {
    50  			a = reflect.Zero(a.Type())
    51  		}
    52  		return reflect.AppendSlice(a, b)
    53  
    54  	case reflect.Struct:
    55  		r := reflect.New(a.Type()) // &struct{}
    56  		for i := 0; i < a.NumField(); i++ {
    57  			v := mergeValue(a.Field(i), b.Field(i))
    58  			r.Elem().Field(i).Set(v)
    59  		}
    60  		return r.Elem() // *struct
    61  
    62  	default:
    63  		panic(fmt.Sprintf("unsupported element type: %v", a.Type()))
    64  	}
    65  }