How to Initialize a Slice of Pointers to Structs in Go: A Breakdown of Anonymous Struct Syntax?

Initializing Slice of Pointers: Understanding Anonymous Struct Syntax

In Chapter 7 of GOPL, an example is given for initializing a slice of pointers to Track structs:

var tracks = []*Track{
    {"Go", "Delilah", "From the Roots Up", 2012, length("3m38s")},
    {"Go", "Moby", "Moby", 1992, length("3m37s")},
    {"Go Ahead", "Alicia Keys", "As I Am", 2007, length("4m36s")},
    {"Ready 2 Go", "Martin Solveig", "Smash", 2011, length("4m24s")},
}

To understand the syntax, let's examine the following code where we define a custom Ex struct and initialize its slices:

type Ex struct {
    A, B int
}

a := []Ex{Ex{1, 2}, Ex{3, 4}}
b := []Ex{{1, 2}, {3, 4}}
c := []*Ex{&Ex{1, 2}, &Ex{3, 4}}
d := []*Ex{{1, 2}, {3, 4}}
e := []*Ex{{1, 2}, &Ex{3, 4}}

In cases a and b, we initialize the slices with instances of the Ex struct using a shortcut syntax:

f := []<type>{{...}, {...}}

This is equivalent to:

f := []<type>{<type>{...}, <type>{...}}

For cases c, d, and e, the syntax requires a bit more explanation. The initialization:

f := []*<type>{{...}, {...}}

Is analogous to:

f := []*<type>{&<type>{...}, &<type>{...}}

In other words, the curly braces following the type specify the values for a struct of that type, and the ampersands create pointers to those structs.

Finally, in the following code, we receive a syntax error:

f := []*Ex{&{1, 2}, &{3, 4}} // Syntax Error!

This is because the curly braces must be followed by the name of a type, not an anonymous struct. The correct syntax would be:

f := []*Ex{&Ex{1, 2}, &Ex{3, 4}}

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