kotlin essentials

kotlin-essentials.md

• var vs val -- mutable vs immutable
• String interpolation -- "String of length ${b.length}"

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• classes -- Backing Fields

var <propertyName>[: <Type>] [= initializer]
                                     [get() = ...]
                                     [set(value) = field = value]

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• function references - :: just like Java
• lambdas: { param1, param2, ... -> block } or { block }
• it -- implicit lambda parameter

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• inline: function attribute keyword
• inline utilities: run, let, takeIf, takeUnless, repeat, withLock, use.
• @InlineOnly => avoids non-inline use of that function
• !!!!! use inline only on small functions ===> be aware of increasing code footprint.
• +++++ Good for higher-order functions avoiding both: 1) allocation and 2) lambdas calls.

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• use() => inline extension to try, finally and close().
• synchronized() == withLock() which is an extension to Lock object

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• Kotlin's type system is aimed to eliminate NullPointerException's

• "leaking this" -- an uninitialized this available in a constructor is passed and used somewhere.

• ? for Nullable -- val variable: Type? = value

• ?. -- safe call -- access member only if not null. Otherwise returns null.

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• Smart casts
• "compiler tracks the is-checks and explicit casts"
• "Safe" (nullable) cast -- val x: String? = y as? String

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• for iterates through anything that provides an iterator(), i.e.
  • has a member- or extension-function iterator()
• return type of iterator() must have:
  • a member- or extension-function next(), and
  • a member- or extension-function hasNext() that returns Boolean.

** All of these three functions need to be marked as operator**

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• Sequence extensions => NOT inlined because of Lazyness
• Collections extensions =>:
  • are extensions for Iterable and return collections like List
  • are inline
• asSequence() like stream() of Java.
• fusion semantics <=> horizontal vs vertical evaluation