Golang variables: Difference between revisions
From wikinotes
(→iota) |
(→iota) |
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Line 47: | Line 47: | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
const ( | const ( | ||
red = iota | red = iota // 0 | ||
green | green // 1 | ||
blue | blue // 2 | ||
) | ) | ||
var color int = red // types within the group will be int now | var color int = red // types within the group will be int now | ||
</syntaxhighlight> | </syntaxhighlight> | ||
Line 61: | Line 58: | ||
Since the type here is inferred, comparing a variable | Since the type here is inferred, comparing a variable | ||
with no value to the first entry will return true. | with no value to the first entry will return true. | ||
for this reason, the first const in a iota group is generally | for this reason, the first const in a iota group is generally discarded or used as an error value. | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
Line 70: | Line 67: | ||
const ( | const ( | ||
_ = iota // this is our trash value -- it's inaccessible | _ = iota // this is our trash value -- it's inaccessible | ||
red | red // 1 | ||
green | green // 2 | ||
blue | blue // 3 | ||
) | |||
</syntaxhighlight> | |||
You can also set the starting value of iota | |||
<syntaxhighlight lang="go"> | |||
const ( | |||
_ = iota + 10 | |||
red // 11 | |||
green // 12 | |||
blue // 13 | |||
) | ) | ||
</syntaxhighlight> | </syntaxhighlight> |
Revision as of 18:45, 29 May 2022
Assignment
// declare and assign variable var name string name = "foo" // declare and assign var in one step var name string = "foo" // declare and assign variable, inferring type name := "foo"
Constants
Basics
const myVar := "hi" // variable that cannot be reassigned const MyVar := "hi" // exported variable, that cannot be reassigned const myVar = 2 // infer constant type const ( // group constant assignment name string = "foo" age int = 123 )There are some rules for constant:
- Constants cannot be assigned at runtime (ex. the result of a function). They must be static at compile time.
- Constants must be assigned a immutable type (ex. collections are mutable, so they cannot be constants)
- Inner scopes can declare the same constant with a new value. It will superseed the outer constant's value while working within that scope.
- If inferring a constant, it's type may take on the type of an operation it is used with. (likely best to explicitly declare type)
iota
iota
will auto-increment the value of the assignment,
allowing you to use constants similar to an enumThe type this constant takes is inferred based on the types it is used with.
const ( red = iota // 0 green // 1 blue // 2 ) var color int = red // types within the group will be int now
Since the type here is inferred, comparing a variable with no value to the first entry will return true. for this reason, the first const in a iota group is generally discarded or used as an error value.// ex. // const ( red = iota; green; blue ) // var i int // i == red // returns true <--- Not what we want!! const ( _ = iota // this is our trash value -- it's inaccessible red // 1 green // 2 blue // 3 )You can also set the starting value of iota
const ( _ = iota + 10 red // 11 green // 12 blue // 13 )
Type Conversion
float32(123) == 123. // cast int as float32 string(107) == "k" // retrieve char for 107 in ascii chart strconv.Itoa(107) == "107" // represent 107 as string
Introspection
fmt.Prinf("%T\n", myVar) // print type of myVar
Mutability
Mutable
- Arrays - Maps - Channels - StructsImmutable
- Interfaces - Booleans - Numeric Types - Strings - Pointers