literal initialization of embeded struct with multiple fields

Question

type fun struct {}

type starcraft struct {
    *fun // embedding struct
    mu sync.Mutex
}

I know I can literal initial struct startcraft as:

f := &fun{}
s := starcraft{f, *new(sync.Mutex)}

I don't like it, since:

a. I don't want to initialize sync.Mutex by myself

b. in this case there is a wasted copy using *new(sync.Mutex).

Is there any better way?

@rvignacio: there's nothing particularly wrong with embedding a pointer to a struct. It might be more convenient if that embedded type is always referenced via a pointer, so you don't need to selectively dereference it or worry about inadvertently creating copies. — Mr_Pink
– Mr_Pink, Commented Jul 16, 2014 at 17:40
@JimB, I thought so at first, but there seems to be no difference between embedding by reference or value (I believe the runtime resolves the derreferencing)... I'm going to write a question about that =P — rvignacio
– rvignacio, Commented Jul 16, 2014 at 20:04
@rvignacio I thought embedding by instance will cause a copy? Please correct me if I am wrong. Can you post your question link to here? — Helin Wang
– Helin Wang, Commented Jul 16, 2014 at 21:17

Mr_Pink · Accepted Answer · 2014-07-16 17:56:58Z

5

You can name embedded structs:

s := starcraft{
    fun: f,
    mu:  *new(sync.Mutex),
}

You don't need to use new to create a zero value. If the type is already declared, you don't need to initialize it at all, or you can use the zero value.

s := starcraft{
    fun: f,
    mu:  sync.Mutex{},
}

And since the zero value for a Mutex is a valid, unlocked Mutex (http://golang.org/pkg/sync/#Mutex), you definitely don't need to initialize it, and can leave it out of the struct literal.

s := starcraft{
    fun: f,
}

On top of that, it's also very common to embed the Mutex and call Lock and Unlock directly on the outer struct.

edited Jul 16, 2014 at 17:56

answered Jul 16, 2014 at 17:33

Mr_Pink

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Comments

Nick Craig-Wood · Accepted Answer · 2014-07-16 16:32:22Z

2

Embedded structs can be named, which suggests this method

f := &fun{}
s := starcraft{fun:f}

Which might be what you want

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answered Jul 16, 2014 at 16:32

Nick Craig-Wood

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1 Comment

Helin Wang Over a year ago

thanks this is also a good answer, accepted JimB's for more information.

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