This is a creation in Article, where the information may have evolved or changed.
Golang Study notes for easy follow-up review.
Variable
Variables are the most basic constituent elements in almost all programming languages. Essentially, a variable is a name for a piece of data storage space, and the program can request a chunk of data storage by defining a variable, and then use that storage space by referencing the variable name.
The use of variables in the go language is similar to that of the C language, but with greater flexibility.
Variable declaration
The variable declaration of the go language differs significantly from the C and C + + languages. For a purely variable declaration, the Go language introduces the keyword VAR, and the type information is placed after the variable name, as shown in the following example:
var v1 int
var v2 stringvar v3 [ten] int//array var v4 [] Int//array slice var v5 struct {
F int}
var V6 *int//Hands
var v7 map[string]intvar V8 func (a int) int//Map,key to String type, value int type
A variable declaration statement does not need to use a semicolon as a terminator. In contrast to the C language, the go language rejects the habit of having to use semicolons as a statement end tag.
Variable initialization
The var keyword can be preserved for scenarios that require initialization when declaring variables, but are no longer necessary elements, as follows:
var v1 int = 10//correct mode of use 1
var v2 = 10//correct mode of use 2, the compiler can automatically deduce the type of V2
V3: = 10//correct mode of use 3, the compiler can automatically deduce the type of V3
The effect of the above three usages is exactly the same. The third use, compared to the first, requires a much lower number of characters to be entered, and is the best choice for lazy programmers and smart programmers. The Go language also introduces another symbol that is not in C and C + + (a combination of colons and equal signs: =), which is used to explicitly express the work of declaring and initializing variables at the same time.
The specified type is no longer required, and the go compiler can deduce from the right value of the initialization expression that the variable should be declared as 4
Which type, which makes the go language look a bit like a dynamic type language, although the go language is actually a no-compromise strongly typed language (statically typed language).
Of course, the variable that appears on the left side should not have been declared, or it will cause a compilation error, such as the following:
var i inti: = 2
Results in a compilation error similar to the following:
No new variables on left side of: =
Variable assignment in Go syntax, variable initialization and variable assignment are two different concepts. The following is the assignment after declaring a variable
Process:
var v10 intv10 = 123
The variable assignment of the Go language is consistent with most languages, but the Go language provides the multi-assignment capabilities that C + + programmers expect for years, such as the following statements that Exchange I and J variables:
I, j = j, I
In languages that do not support multiple assignments, the content of the interactive two variables requires the introduction of an intermediate variable:
t = i; i = j; j = t;
Anonymous variables
When we are programming with traditional strongly typed languages, this is often the case when a function is called in order to get a value, but because the function returns multiple values, it has to define a bunch of useless variables. In go, this can be done by combining multiple returns and anonymous variables to avoid this ugly notation and make the code look more elegant.
_, _, Nickname: = "may", "Chan", "Chibi Maruko"
Constant
In the go language, constants refer to values that are known and immutable during compilation. Constants can be numeric types (including integer, float, and complex types), Boolean types, string types, and so on.
Literal constants
The so-called Literal constants (literal) refer to hard-coded constants in the program, such as:
-12
3.14159265358979323846//constant of floating-point type 3.2+12i//constant of plural type true//Boolean type constant "foo"//String constant
The literal constants of the go language are closer to the constant concept in our natural language, which is untyped. As long as the constant is within the range of the corresponding type, it can be used as a constant of that type, such as the above constant 12, which can be assigned to variables of type int, uint, Int32, Int64, float32, float64, complex64, complex128, and so on.
Constant definition
With the const keyword, you can specify a friendly name for literal constants:
Const Pi float64 = 3.14159265358979323846
Const ZERO = 0.0
Const U, v float32 = 0, 3
Const A, b, C = 3, 4, "foo"//a=3,b=4,c= "foo", untyped integer and string constant
The constant definition of go can qualify a constant type, but is not required. If you define a constant without specifying a type, it is, like a literal constant, an untyped constant. The right-hand value of a constant definition can also be a constant expression that is evaluated at compile time, such as:
Const MASK = 1 << 3 Because the assignment of a constant is a compile-time behavior, an rvalue cannot have any expression that requires a run time to produce a result, such as attempting to define a constant in such a way as to cause a compilation error:
Const HOME = os. GETENV ("HOME")
The reason is simple, os. GETENV () The return result is known only at run time and cannot be determined at compile time, so the right value cannot be defined as a constant.
Pre-defined constants
Go The language pre-defines these constants: true , false and the Iota . Iota is special and can be thought of as a constant that can be modified by the compiler, defined by constants when each const keyword appears .
With the const keyword, you can specify a friendly name for literal constants:
Const Pi float64 = 3.14159265358979323846//No type floating-point constant//untyped integer constant
Const U, v float32 = 0, 3
Const A, b, C = 3, 4, "foo"//a=3,b=4,c= "foo", untyped integer and string constant
Const ZERO = 0.0
The constant definition of go can qualify a constant type, but is not required. If you define a constant without specifying a type, it is, like a literal constant, an untyped constant. The right-hand value of a constant definition can also be a constant expression that is evaluated at compile time, such as
Const MASK = 1 << 3
Because the assignment of a constant is a compile-time behavior, an rvalue cannot have any expression that requires a run time to produce a result, such as attempting to define a constant in such a way as to cause a compilation error:
Const HOME = os. GETENV ("HOME")
The reason is simple, os. GETENV () The returned result is only known at run time, is not determined at compile time, is reset to 0, and then the number represented by the next const appears to be increased by 1, each time it appears iota. The following example can be used to understand the usage of iota basically:
The following example can be used to understand the usage of iota basically:
Const (
C0 = Iota//iota is reset to 0//C0 = = 0
C1 = IOTA//C1 = = 1
C2 = Iota//C2 = = 2
）
Const (
A = 1 << iota//A = = 1 (iota is reset to 0 at the beginning of each const)
b = 1 << iota//b = = 2
c = 1 << iota//c = = 4
)
Type
Go The following basic types are built into the language:
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