What is the implementation principle of Go iota keyword and enumeration type

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1. iota keyword

iota is a constant counter in go language, which can only be used in constant expressions. Its value starts from 0. Each new line of iota in const increases by 1, and its value keeps increasing by 1 until it encounters the next one.const keyword, its value is reset to 0.

const ( a int = iota // 0 b b // 1 c c // 2 d d // 3)

In addition, when using iota, you can skip certain lines (it should be noted that spaces are not counted as lines).

const ( a = iota // 0 b b // 1 c c // 5 )

Also, iota can participate in mathematical operations.

 Type Allergen Intconst (Igeggs Allergen = 1 << ota // 1 << 0 Which is 00000001 = 1 igChocolate // 1 << 1 WHICH is 0000000010 = 2 ignuts // 1 << 2 which is 00000100 = 4 IgStrawberries // 1 << 3 which is 00001000 = 8 IgShellfish // 1 << 4 which is 00010000 = 16)

And, on the same line, an iota can be used multiple times:

 const (a, q int = IOTA, IoTa+1 // 0, 1 B, W // 1, 2 c, E/2, 3 d, r // 3, 4)

In summary, we can find that iota is similar to a line count in a const (), when we call it, no matter how many times we use it or not, itap will count each lineDo a count.

2. Enumeration type

Enumerations are used to represent types that contain only a limited number of fixed values, and are generally used in development to identify error codes or state machines.Take the state machine of an entity object, which usually corresponds to the field value of the object's corresponding record in the database that identifies the state.

Java provides us with ready-made implementations of enum classes.But not in Go, so we can use type to define a type and combine iota to achieve the effect of enumeration class:

type Season intconst ( Summer Season = 1 Autumn = 2 Winter = 3 Spring = 4)

Although the underlying implementation is still the int type, when we use the int type to compare directly with the Season type variable, there will be an error that the compilation fails, so that we can make type restrictions on the enumeration types we need.

Of course, we can also combine the above-mentioned itao to optimize:

type Season intconst (Summer Season = iota + 1 Autumn     Winter     Spring     )

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