Init array of structs in Go

Question

I'm newbie in Go. This issue is driving me nuts. How do you init array of structs in Go?

type opt struct {     shortnm      char     longnm, help string     needArg      bool }  const basename_opts []opt {          opt {             shortnm: 'a',              longnm: "multiple",              needArg: false,              help: "Usage for a"}         },         opt {             shortnm: 'b',              longnm: "b-option",              needArg: false,              help: "Usage for b"}     } 

The compiler said it expecting ; after []opt.

Where should I put the braces { to init my array of struct?

Answer 1

It looks like you are trying to use (almost) straight up C code here. Go has a few differences.

• First off, you can't initialize arrays and slices as const. The term const has a different meaning in Go, as it does in C. The list should be defined as var instead.
• Secondly, as a style rule, Go prefers basenameOpts as opposed to basename_opts.
• There is no char type in Go. You probably want byte (or rune if you intend to allow unicode codepoints).
• The declaration of the list must have the assignment operator in this case. E.g.: var x = foo.
• Go's parser requires that each element in a list declaration ends with a comma. This includes the last element. The reason for this is because Go automatically inserts semi-colons where needed. And this requires somewhat stricter syntax in order to work.

For example:

type opt struct {     shortnm      byte     longnm, help string     needArg      bool }  var basenameOpts = []opt {      opt {         shortnm: 'a',          longnm: "multiple",          needArg: false,          help: "Usage for a",     },     opt {         shortnm: 'b',          longnm: "b-option",          needArg: false,          help: "Usage for b",     }, } 

An alternative is to declare the list with its type and then use an init function to fill it up. This is mostly useful if you intend to use values returned by functions in the data structure. init functions are run when the program is being initialized and are guaranteed to finish before main is executed. You can have multiple init functions in a package, or even in the same source file.

    type opt struct {         shortnm      byte         longnm, help string         needArg      bool     }      var basenameOpts []opt      func init() {          basenameOpts = []opt{             opt {                 shortnm: 'a',                  longnm: "multiple",                  needArg: false,                  help: "Usage for a",             },             opt {                 shortnm: 'b',                  longnm: "b-option",                  needArg: false,                 help: "Usage for b",             },         }     } 

Since you are new to Go, I strongly recommend reading through the language specification. It is pretty short and very clearly written. It will clear a lot of these little idiosyncrasies up for you.

Answer 2

Adding this just as an addition to @jimt's excellent answer:

one common way to define it all at initialization time is using an anonymous struct:

var opts = []struct {     shortnm      byte     longnm, help string     needArg      bool }{     {'a', "multiple", "Usage for a", false},     {         shortnm: 'b',         longnm:  "b-option",         needArg: false,         help:    "Usage for b",     }, } 

This is commonly used for testing as well to define few test cases and loop through them.