Go Concepts - Lexical Structure: Difference between revisions
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Pre-declared zero value: <tt>nil</tt>. | Pre-declared zero value: <tt>nil</tt>. | ||
==The Blank Identifier== | |||
"_" is the blank identifier. | |||
=Types= | =Types= |
Revision as of 02:01, 23 March 2016
Internal
Source Files
Go code goes into source files. They have the .go extension.
Each source file is mandatory declared to belong to a package.
They can then optionally import code from other packages, using the import keyword.
Comments
// to the end of the line
/* Multiline line 1 ... line n */
Whitespace
Whitespace in Go are carriage returns (u+000D), newlines (u+000A), spaces (u+0020) and tabs (u+0009).
Semicolons
Go programs may omit most of the semicolons at the end of line if the following conditions apply:
- When the input is broken into tokens, a semicolon is automatically inserted into the token stream immediately after a line's final token if that token is:
- an identifier
- an integer, floating-point, imaginary, rune, or string literal
- one of the keywords break, continue, fall through, or return
- one of the operators and delimiters ++, --, ), ], or }
- To allow complex statements to occupy a single line, a semicolon may be omitted before a closing ")" or "}".
For more details, see the specification:
Identifiers
Identifiers name program entities, such as constants, variables, types, functions, etc. An identifier is a sequence of one more letter and digits. The first character must be a letter. The letters are unicode letters or underscore "_".
Identifiers can be exported. See exported identifiers.
Pre-Declared Identifiers
Pre-declared identifiers are available by default, without needing to import anything. They are implicitly declared in the universe block.
Pre-declared types: bool, byte, complex64, complex128, float32, float64, int, int8, int16, int32, int64, rune, string, uint, uint8, uint16, uint32, uint64, uintptr and error.
Pre-declared constants: true, false, iota.
Pre-declared functions: append, cap, close, complex, copy, delete, imag, len, make, new, panic, print, println, real, recover. Also see built-in functions.
Pre-declared zero value: nil.
The Blank Identifier
"_" is the blank identifier.
Types
Constants
Functions
Operators
Expression
Operators combine operands into expressions.
Literal
A literal is a notation for representing a fixed value in source code. Go provides literals for booleans, integers, floating-point values, strings, built-in types such as arrays, slices and maps, user-defined types (structs), functions, etc.
Statements
- Go Language Specification https://golang.org/ref/spec#Statements
Statements control execution flow within a function.
for
if
Keywords
- Go Specification - Keywords: https://golang.org/ref/spec#Keywords
range | type | func | . | . |
package | go | . | . | . |
defer | chan | import | . | . |
Variables
Variables are always initialized to the type's zero value.
var <var-name> <type> = <initial-value> var a string = "blah"
<var-name> := <initial-value> a := "blah"
Variable Scopes
Package-level variable
Pass by Value vs Pass by Reference
In Go, all variables are passed by value. Even for pointer variables, since the value of the pointer is a memory address, passing pointer variables is still considered pass by value.
Pointers
Pointer variable.