为什么文字值没有类型？
Why literal value has no type?
类型推断是Swift的强大属性。这意味着编译器可以从程序员提供的值中推断出文字的类型，不需要显式类型说明。
例如var IntNum = 3；编译器可以推断变量 IntNum 是 Int 类型。在 Xcode 中，如果用户按下键并单击变量名称，这里 IntNum，那么 Xcode 会告诉你它是什么类型。
但是，如果我对字面值 3 执行此操作，Xcode 什么也不会提供。我想，我放在屏幕上的文字值根本就没有类型，只有对象变量和常量的类型是 属性。
我猜是这样，谁能给我解释一下？
干杯
SL
没错。
Type Safety and Type Inference
Type inference is particularly useful when you declare a constant or
variable with an initial value. This is often done by assigning a
literal value (or literal) to the constant or variable at the point
that you declare it. (A literal value is a value that appears directly
in your source code)
...
If you combine integer and floating-point literals in an expression, a
type of Double will be inferred from the context:
let anotherPi = 3 + 0.14159
// anotherPi is also inferred to be of type Double
The literal value of 3 has no explicit type in and of itself, and so
an appropriate output type of Double is inferred from the presence of
a floating-point literal as part of the addition.
类型推断是Swift的强大属性。这意味着编译器可以从程序员提供的值中推断出文字的类型，不需要显式类型说明。
例如var IntNum = 3；编译器可以推断变量 IntNum 是 Int 类型。在 Xcode 中，如果用户按下键并单击变量名称，这里 IntNum，那么 Xcode 会告诉你它是什么类型。
但是，如果我对字面值 3 执行此操作，Xcode 什么也不会提供。我想，我放在屏幕上的文字值根本就没有类型，只有对象变量和常量的类型是 属性。
我猜是这样，谁能给我解释一下？
干杯 SL
没错。
Type Safety and Type Inference
Type inference is particularly useful when you declare a constant or variable with an initial value. This is often done by assigning a literal value (or literal) to the constant or variable at the point that you declare it. (A literal value is a value that appears directly in your source code)
...
If you combine integer and floating-point literals in an expression, a type of Double will be inferred from the context:
let anotherPi = 3 + 0.14159 // anotherPi is also inferred to be of type DoubleThe literal value of 3 has no explicit type in and of itself, and so an appropriate output type of Double is inferred from the presence of a floating-point literal as part of the addition.