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Crystal / Collections

select

Learn select in Crystal with a construct-specific explanation, unique example, engineering boundary, and mastery check.

10 min read • Intermediate

select is a focused Crystal topic inside Collections. This lesson explains the construct itself, the state or value it operates on, and the observable result it produces.

Read the example as a small executable experiment. Identify the exact syntax that belongs to select, then change one input and predict the result before running it.

Topic-specific example

crystal-05-07-select.cr
crystal Try It Live 
p [1,2,3,4,5].select { |x| x.odd? }
Edge case / engineering note

select has rules that are easy to miss when the example is copied mechanically. Check the feature-specific boundary shown by this construct: scope, mutability, evaluation order, type constraints, lifetime, error behavior, compile-time restrictions, or resource cleanup where applicable.

Content source & attribution
Original Syntaxis Content · Original Syntaxis Content

Lesson quizzes

select Mastery Check →
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Enumerable map
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compact_map