Map!
map! is a mutating collection operation that applies a transformation to elements and writes the resulting values into a destination collection.
The Well-Grounded Rubyist, Fourth Edition
map! is a mutating collection method that replaces each element with the value produced by applying a transformation block.
- How it is used
- Transforms existing array or set elements in place rather than collecting a new array with map.
- How deep it goes
- Defines in-place mapping and contrasts its receiver types with map, without detailing map!’s implementation or return value.
- Examples
- Shows an array of names changed in place with `names.map!(&:upcase)`.
- What you can do after
- Apply it via Ruby’s Array#map! or Set#map! when the collection itself should change.
Read how The Well-Grounded Rubyist, Fourth Edition explains map! →
Julia as a Second Language
map! is a Julia mutating mapping function that writes transformed elements into a destination array.
- How it is used
- Reuses a preallocated array while transforming a collection, avoiding a new array for each mapping.
- How deep it goes
- Explains argument order and demonstrates two successive mappings, but does not develop a broader procedure for managing mutation.
- Examples
- Uses a sine table that converts degree values to radians, then replaces them with sine values in one array.
- What you can do after
- Apply it via Julia’s map! to write transformations into a destination array and, when suitable, reuse that array as input.
Related concepts
- higher-order functionkind of · A higher-order function is a function that accepts functions as arguments, returns functions as results, or both.
- each_entrycontrasts with · each_entry is a Ruby enumeration method that yields each element of a collection to a block.
- blockuses · A code block is a grouped region of code treated as a unit, with boundaries and scope or execution behavior determined by its language or context.
- enumeratorproduces · An enumerator is a Ruby object that represents and controls iteration over an enumerable source, optionally allowing iteration without supplying a block immediately.
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