What is the difference between let
and var
in Apple’s Swift language?
In my understanding, it is a compiled language but it does not check the type at compile time. It makes me confused. How does the compiler know about the type error? If the compiler doesn’t check the type, isn’t it a problem with production environment?
This error is given when I try to assign a value to a let
:
Cannot assign to property: ‘variableName’ is a ‘let’ constant
Change ‘let’ to ‘var’ to make it mutable
32 Answers
The let
keyword defines a constant:
let theAnswer = 42
The theAnswer
cannot be changed afterwards. This is why anything weak
can’t be written using let
. They need to change during runtime and you must be using var
instead.
The var
defines an ordinary variable.
What is interesting:
The value of a constant doesn’t need to be known at compile time, but you must assign the value exactly once.
Another strange feature:
You can use almost any character you like for constant and variable
names, including Unicode characters:
let 🐶🐮 = "dogcow"
Excerpts From: Apple Inc. “The Swift Programming Language.” iBooks. https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewBook?id=881256329
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