Golang variables: Difference between revisions
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= Environment Variables = | = Process Variables = | ||
<blockquote> | |||
== Call Parameters == | |||
<blockquote> | |||
commandline arguments are stored in <code>os.Args</code> | |||
<syntaxhighlight lang="go"> | |||
for _, arg := range os.Args[1:] { | |||
switch arg { | |||
case "-h", "--help": | |||
// .. print help | |||
case "-v", "--verbose": | |||
// .. enable verbose logging | |||
} | |||
} | |||
</syntaxhighlight> | |||
</blockquote><!-- Call Parameters --> | |||
== Environment Variables == | |||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- Environment Variables --> | </blockquote><!-- Environment Variables --> | ||
</blockquote><!-- Process Variables --> | |||
= Assignment = | = Go Variables = | ||
<blockquote> | |||
== Assignment == | |||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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</blockquote><!-- Assignment --> | </blockquote><!-- Assignment --> | ||
= Scope = | == Scope == | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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</blockquote><!-- Scope --> | </blockquote><!-- Scope --> | ||
= Type Conversion = | == Type Conversion == | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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</blockquote><!-- Type Conversion --> | </blockquote><!-- Type Conversion --> | ||
= Introspection = | == Introspection == | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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= Constants = | == Constants == | ||
<blockquote> | <blockquote> | ||
== Basics == | === Basics === | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="go"> | <syntaxhighlight lang="go"> | ||
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</blockquote><!-- Basics --> | </blockquote><!-- Basics --> | ||
== iota == | === iota === | ||
<blockquote> | <blockquote> | ||
See enums in [[golang datatypes]] | See enums in [[golang datatypes]] | ||
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</blockquote><!-- Constants --> | </blockquote><!-- Constants --> | ||
= Mutability = | == Mutability == | ||
<blockquote> | <blockquote> | ||
== Mutable == | === Mutable === | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="yaml"> | <syntaxhighlight lang="yaml"> | ||
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</blockquote><!-- Mutable --> | </blockquote><!-- Mutable --> | ||
== Immutable == | === Immutable === | ||
<blockquote> | <blockquote> | ||
<syntaxhighlight lang="yaml"> | <syntaxhighlight lang="yaml"> | ||
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</blockquote><!-- Immutable --> | </blockquote><!-- Immutable --> | ||
</blockquote><!-- Mutability --> | </blockquote><!-- Mutability --> | ||
</blockquote><!-- Go Variables --> |
Revision as of 22:20, 18 June 2022
Process Variables
Call Parameters
commandline arguments are stored in
os.Args
for _, arg := range os.Args[1:] { switch arg { case "-h", "--help": // .. print help case "-v", "--verbose": // .. enable verbose logging } }Environment Variables
import "os" path, err := os.LookupEnv("HOME") // "/home/will" err := os.SetEnv("FOO", "BAR") vars = os.Environ() // ["FOO=BAR", "BAR=BAZ", ...]
Go Variables
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"Scope
// global variables are defined outside of functions foo_global := "bar" // local variables defined in functions func main() { foo_local := "bar" }go supports closures (although to be async friendly, it is recommended to explicitly pass params)
func main() { a := 123 func() { fmt.Println("value of a:", a) } }Exported symbols (functions, variables) begin with a capital letter.
this means they can be used by files that import this package.Foo := "bar" func MyPublicFunc() { ... }Exported symbols from packages defined within an
internal/
directory are only exported within your go module.
Consumers of your go module and it's packages will not have access to these symbols.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 stringIntrospection
fmt.Prinf("%T\n", myVar) // print type of myVar
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
See enums in golang datatypes
Mutability
Mutable
- Arrays - Maps - Channels - StructsImmutable
- Interfaces - Booleans - Numeric Types - Strings - Pointers