Struct field not updated when implementing interface function

Question

If for example we have the following interface:

type IRoute interface {
    AddChildren(child IRoute)
}

The following struct:

type Route struct {
    Alias string `json:"alias"`
    Children []Route `json:"children,omitempty"`
    Url string `json:"url,omitempty"`
}

And implemented the interface:

func (this Route) AddChildren (child globals.IRoute){
    this.Children = append(this.Children, child.(Route))
}

Then in our main func, if we wanted to test this it would not work:

rSettings := Route{"settings", nil, "/admin/settings"}
rSettingsContentTypesNew := models.Route{"new", nil, "/new?type&parent"}
rSettingsContentTypesEdit := models.Route{"edit", nil, "/edit/:nodeId"}

// Does NOT work - no children is added
rSettingsContentTypes.AddChildren(rSettingsContentTypesNew)
rSettingsContentTypes.AddChildren(rSettingsContentTypesEdit)
rSettings.AddChildren(rSettingsContentTypes)

And this does work as expected:

rSettings := Route{"settings", nil, "/admin/settings"}
rSettingsContentTypesNew := models.Route{"new", nil, "/new?type&parent"}
rSettingsContentTypesEdit := models.Route{"edit", nil, "/edit/:nodeId"}

// However this does indeed work
rSettingsContentTypes.Children = append(rSettingsContentTypes.Children,rSettingsContentTypesNew)
rSettingsContentTypes.Children = append(rSettingsContentTypes.Children,rSettingsContentTypesEdit)
rSettings.Children = append(rSettings.Children,rSettingsContentTypes)

What am I missing? :-)

Kiril · Accepted Answer · 2015-02-13 10:28:39Z

5

The receiver of func (this Route) AddChildren (child globals.IRoute) is a value, so you are changing a copy of your Route struct.

Change it to func (this *Route) AddChildren (child globals.IRoute)

edited Feb 13, 2015 at 10:28

answered Feb 13, 2015 at 10:23

Kiril

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1 Comment

Kiril Over a year ago

Happy I could help. Here is a little further reading: golang.org/doc/faq#Pointers and for this specific question golang.org/doc/faq#methods_on_values_or_pointers

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