How deeply does Kotlin in Action, 2E cover constructor parameter?

Explains concise and explicit declarations, initializer blocks, property promotion, defaults, named arguments, inheritance, and private constructors.

Constructor parameter

As explained in Kotlin in Action, 2E

A constructor parameter is a parameter declared by a Kotlin constructor and optionally promoted to a property.

A constructor parameter supplies values when a Kotlin object is created. Prefixing it with val or var also promotes it to a property, keeping simple class declarations compact. section 4.2.1

class User(val nickname: String)

This compact declaration accepts a nickname and exposes it as a read-only property. section 4.2.1

Default and named arguments

class User( val nickname: String, val isSubscribed: Boolean = true ) User("Alice") User("Bob", false) User("Carol", isSubscribed = false) A parameter can therefore provide a default value, accept positional input, or be selected by name. section 4.2.1

Use an explicit form when initialization needs more structure:

Declare a parameter without val or var when it only supplies initialization data. section 4.2.1
Refer to primary-constructor parameters from property initializers and initializer blocks. section 4.2.1
Pass constructor parameters to a superclass when declaring a subclass. section 4.2.1

How Kotlin in Action, 2E covers it

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Related concepts

dependency injectionused by · Dependency injection is a software design technique in which a component receives its dependencies from outside rather than creating or locating them internally.
primary constructorpart of · A primary constructor is the constructor declared in a Kotlin class header that specifies constructor parameters and can define properties initialized from them.

This explainer was generated by Manning's knowledge graph from the text of Kotlin in Action, 2E. The section links point to the parts of the book it draws on.