Range loop
A range loop is a Go for-loop form that iterates over values or entries produced by a supported rangeable expression.
100 Go Mistakes and How to Avoid Them
A range loop is a Go loop construct that iterates over elements of an array, slice, map, string, pointer to an array, or receiving channel.
- How it is used
- Uses range loops to expose mistakes involving copied values, one-time expression evaluation, pointers, and string iteration.
- How deep it goes
- Works through observable results and contextual fixes for slices, arrays, channels, pointers, maps, and strings.
- Examples
- Traces unchanged account balances, a growing slice, reassigned channels, an edited array, customer pointers, and the string `"hêllo"`.
- What you can do after
- Diagnose/debug with it when a loop changes copies, reads unexpected values, retains an original channel, or reports byte positions.
Read how 100 Go Mistakes and How to Avoid Them explains range loop →
Go in Action, Second Edition
A range loop is a Go for-loop form that iterates over the elements or entries of a supported collection and can provide each element's index and value.
- How it is used
- Uses range to process collections of variable length, including command-line filenames and race results.
- How deep it goes
- Explains assignment forms, copied values, string indices, and map order; defers channel behavior.
- Examples
- Demonstrates multiple-file word counting, Unicode character positions, race results, and map filtering.
- What you can do after
- Apply it via Go's range clause to traverse variable-length collections and choose indices when modifying array elements.
Go by Example
A for-range loop is a Go loop construct that iterates over values produced by a rangeable expression, including supported iterator functions.
- How it is used
- Consumes iterator-produced values in synchronous APIs while hiding whether the producer uses slices, channels, or concurrent internals.
- How deep it goes
- Explains consumption, depletion, early termination, yield signaling, and nil handling, but stops short of general range syntax.
- Examples
- Uses a Results iterator and a Summarize function that aggregates request outcomes and transferred bytes.
- What you can do after
- Apply it via Go's for-range syntax to consume custom iterators and terminate processing early when appropriate.
Related concepts
- value copyproduces · A value copy is an independently copied element value produced by iteration rather than a writable reference to the original collection element.
- blank identifieruses · A blank identifier is a language-defined name or symbol that receives or matches a value without binding it to a usable variable.
- call by valueproduces · Call by value is a parameter-passing semantics in which a called operation receives its own copy of an argument’s value.
- arrayuses · An array is an indexed, ordered collection of elements arranged in one or more dimensions, with elements accessed by position.
- stringuses · A string is a programming-language value representing an ordered sequence of characters or character units as text.
- Mapuses · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
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