deep-copy

deep-copy is a tool for generating DeepCopy() functions for a given type.

Given a package directory, and a type name that appears in that package, a DeepCopy method will be generated, to create a deep copy of the type value. Members of the type will also be copied deeply, recursively. If a member T of the type has a method DeepCopy() [*]T, that method will be reused. Multiple types can be specified for the given package, by adding more --type parameters.

To specify a pointer receiver for the method, an optional --pointer-receiver boolean flag can be specified. The flag will also govern whether the return type is a pointer as well.

To specify build tags in the generated code, an optional --tags comma separated list flag can be specified. The flag will add all items as build tags to the generated code.

It might also be desirable to skip deeply copying certain fields, slice members, or map members. To achieve that, selectors can be specified in the optional comma-separated --skip flag. Multiple --skip flags can be specified, to match the number of --type flags. For example, given the following type:

type Foo struct {
     J *int
     B Bar
}

type Bar struct {
    I *int
}

Leaving the 'B' field as a shallow copy can be achieved by specifying --skip B. To skip deeply copying the inner 'I' field, one can specify --skip B.I. Slice and Map members can also be skipped, by adding [i] and [k] respectively.

To specify a max depth of deep copying, use --maxdepth option. It stops deep copying at a given depth, with a warning message spotting a place the deep copying has been stopped. It might especially be useful when one or more structs have circular references.

To change a method name of deep copying, use --method option.

Usage

Pass either path to the folder containing the types or the module name:

deep-copy <flags> /path/to/package/containing/type
deep-copy <flags> github.com/globusdigital/deep-copy
deep-copy <flags> github.com/globusdigital/deep-copy/some/sub/packages

Here is the full set of supported flags:

deep-copy \
  [-o /output/path.go] \
  [--method DeepCopy] \
  [--pointer-receiver] \
  [--skip Selector1,Selector.Two --skip Selector2[i], Selector.Three[k]]
  [--type Type1 --type Type2\ \
  [--tags mytag,anotherTag ] \ \
  /path/to/package/containing/type

Example

Given the following types:

package pkg

type Foo struct {
    Map map[string]*Bar
    ch  chan float32
    baz Baz
}

type Bar struct {
    IntV  int
    Slice []string
}

type Baz struct {
    String        string
    StringPointer *string
}

Running deep-copy --type Foo ./path/to/pkg will generate:

// Code generated by deep-copy --type Foo ./path/to/pkg; DO NOT EDIT.

package pkg

// DeepCopy generates a deep copy of Foo
func (o Foo) DeepCopy() Foo {
    var cp Foo
    cp = o
    if o.Map != nil {
        cp.Map = make(map[string]*Bar, len(o.Map))
        for k, v := range o.Map {
            var cpv *Bar
            if v != nil {
                cpv = new(Bar)
                *cpv = *v
                if v.Slice != nil {
                    cpv.Slice = make([]string, len(v.Slice))
                    copy(cpv.Slice, v.Slice)
                }
            }
            cp.Map[k] = cpv
        }
    }
    if o.ch != nil {
        cp.ch = make(chan float32, cap(o.ch))
    }
    if o.baz.StringPointer != nil {
        cp.baz.StringPointer = new(string)
        *cp.baz.StringPointer = *o.baz.StringPointer
    }
    return cp
}