Let keyword
A let construct is a language feature that introduces a name binding associating an identifier with a value or expression.
Rust in Action: Systems programming concepts and techniques
A let binding introduces a local Rust variable binding whose associated value may have internally mutable state even when the binding itself is immutable.
- How it is used
- Declares local bindings in Rust programs, including values used in arithmetic and function calls.
- How deep it goes
- Explains declaration syntax, type annotations, default immutability, and its distinction from interior mutability and borrowing; it does not develop those mechanisms further.
- Examples
- Uses an integer-addition program with several declaration forms and `Arc` and `Rc` reference counts as a contrasting case.
- What you can do after
- Evaluate/understand whether a Rust declaration needs an explicit type and why an immutable binding can hold internally changing state.
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Learn Haskell by Example
A let binding is a local Haskell definition that associates an identifier with an expression or function definition.
- How it is used
- Uses local immutable definitions to clarify expressions, actions, transformations, and recursive implementations.
- How deep it goes
- Explains expression and do-notation forms, local functions, scope, immutability, and declarative decomposition.
- Examples
- Demonstrates uppercase input, arithmetic in GHCi, line numbering, and human-readable formatting of optional numbers.
- What you can do after
- Apply let bindings to name intermediate values, structure local helpers, and hide implementation parameters.
Related concepts
- shadowingused by · Shadowing is the concealment of an existing name binding or inherited property by a nearer declaration or property with the same name.
- variableuses · A variable is a named program binding or entity associated with a value that can be accessed and, when permitted, changed during computation.
- const qualifiercontrasts with · A language feature that marks a value, binding, or access path as constant, restricting reassignment or modification according to the language’s rules.
- local functionuses · A local function is a named function declared within another function or local scope and accessible within that enclosing lexical context.
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