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Diffstat (limited to 'spec/05-classes-and-objects.md')
| -rw-r--r-- | spec/05-classes-and-objects.md | 103 |
1 files changed, 53 insertions, 50 deletions
diff --git a/spec/05-classes-and-objects.md b/spec/05-classes-and-objects.md index 65666e31cb..ffb65979f7 100644 --- a/spec/05-classes-and-objects.md +++ b/spec/05-classes-and-objects.md @@ -7,9 +7,9 @@ chapter: 5 # Classes and Objects ```ebnf -TmplDef ::= [`case'] `class' ClassDef - | [`case'] `object' ObjectDef - | `trait' TraitDef +TmplDef ::= [‘case’] ‘class’ ClassDef + | [‘case’] ‘object’ ObjectDef + | ‘trait’ TraitDef ``` [Classes](#class-definitions) and [objects](#object-definitions) @@ -20,14 +20,14 @@ are both defined in terms of _templates_. ```ebnf ClassTemplate ::= [EarlyDefs] ClassParents [TemplateBody] TraitTemplate ::= [EarlyDefs] TraitParents [TemplateBody] -ClassParents ::= Constr {`with' AnnotType} -TraitParents ::= AnnotType {`with' AnnotType} -TemplateBody ::= [nl] `{' [SelfType] TemplateStat {semi TemplateStat} `}' -SelfType ::= id [`:' Type] `=>' - | this `:' Type `=>' +ClassParents ::= Constr {‘with’ AnnotType} +TraitParents ::= AnnotType {‘with’ AnnotType} +TemplateBody ::= [nl] ‘{’ [SelfType] TemplateStat {semi TemplateStat} ‘}’ +SelfType ::= id [‘:’ Type] ‘=>’ + | this ‘:’ Type ‘=>’ ``` -A template defines the type signature, behavior and initial state of a +A _template_ defines the type signature, behavior and initial state of a trait or class of objects or of a single object. Templates form part of instance creation expressions, class definitions, and object definitions. A template @@ -145,7 +145,7 @@ def delayedInit(body: => Unit) ### Constructor Invocations ```ebnf -Constr ::= AnnotType {`(' [Exprs] `)'} +Constr ::= AnnotType {‘(’ [Exprs] ‘)’} ``` Constructor invocations define the type, members, and initial state of @@ -344,8 +344,8 @@ $M'$: - If $M$ and $M'$ are both concrete value definitions, then either none of them is marked `lazy` or both must be marked `lazy`. -A stable member can only be overridden by a stable member. -For example, this is not allowed: +- A stable member can only be overridden by a stable member. + For example, this is not allowed: ```scala class X { val stable = 1} @@ -410,7 +410,7 @@ necessary to make subtyping decidable[^kennedy]). ### Early Definitions ```ebnf -EarlyDefs ::= `{' [EarlyDef {semi EarlyDef}] `}' `with' +EarlyDefs ::= ‘{’ [EarlyDef {semi EarlyDef}] ‘}’ ‘with’ EarlyDef ::= {Annotation} {Modifier} PatVarDef ``` @@ -478,14 +478,14 @@ body, it would be initialized after the constructor of ```ebnf Modifier ::= LocalModifier | AccessModifier - | `override' -LocalModifier ::= `abstract' - | `final' - | `sealed' - | `implicit' - | `lazy' -AccessModifier ::= (`private' | `protected') [AccessQualifier] -AccessQualifier ::= `[' (id | `this') `]' + | ‘override’ +LocalModifier ::= ‘abstract’ + | ‘final’ + | ‘sealed’ + | ‘implicit’ + | ‘lazy’ +AccessModifier ::= (‘private’ | ‘protected’) [AccessQualifier] +AccessQualifier ::= ‘[’ (id | ‘this’) ‘]’ ``` Member definitions may be preceded by modifiers which affect the @@ -597,10 +597,12 @@ overridden in subclasses. A `final` class may not be inherited by a template. `final` is redundant for object definitions. Members of final classes or objects are implicitly also final, so the `final` modifier is generally redundant for them, too. Note, however, that -[constant value definitions](04-basic-declarations-and-definitions.html#value-declarations-and-definitions) do require -an explicit `final` modifier, even if they are defined in a final class or -object. `final` may not be applied to incomplete members, and it may not be -combined in one modifier list with `sealed`. +[constant value definitions](04-basic-declarations-and-definitions.html#value-declarations-and-definitions) +do require an explicit `final` modifier, +even if they are defined in a final class or object. +`final` is permitted for abstract classes +but it may not be applied to traits or incomplete members, +and it may not be combined in one modifier list with `sealed`. ### `sealed` The `sealed` modifier applies to class definitions. A @@ -668,16 +670,16 @@ constructor `private` ([example](#example-private-constructor)). ## Class Definitions ```ebnf -TmplDef ::= `class' ClassDef +TmplDef ::= ‘class’ ClassDef ClassDef ::= id [TypeParamClause] {Annotation} [AccessModifier] ClassParamClauses ClassTemplateOpt ClassParamClauses ::= {ClassParamClause} - [[nl] `(' implicit ClassParams `)'] -ClassParamClause ::= [nl] `(' [ClassParams] ')' -ClassParams ::= ClassParam {`,' ClassParam} -ClassParam ::= {Annotation} {Modifier} [(`val' | `var')] - id [`:' ParamType] [`=' Expr] -ClassTemplateOpt ::= `extends' ClassTemplate | [[`extends'] TemplateBody] + [[nl] ‘(’ implicit ClassParams ‘)’] +ClassParamClause ::= [nl] ‘(’ [ClassParams] ‘)’ +ClassParams ::= ClassParam {‘,’ ClassParam} +ClassParam ::= {Annotation} {Modifier} [(‘val’ | ‘var’)] + id [‘:’ ParamType] [‘=’ Expr] +ClassTemplateOpt ::= ‘extends’ ClassTemplate | [[‘extends’] TemplateBody] ``` The most general form of class definition is @@ -709,7 +711,7 @@ Here, value parameter may not form part of the types of any of the parent classes or members of the class template $t$. It is illegal to define two formal value parameters with the same name. - If no formal parameter sections are given, an empty parameter section `()` is assumed. + If a class has no formal parameter section that is not implicit, an empty parameter section `()` is assumed. If a formal parameter declaration $x: T$ is preceded by a `val` or `var` keyword, an accessor (getter) [definition](04-basic-declarations-and-definitions.html#variable-declarations-and-definitions) @@ -725,7 +727,7 @@ Here, - $t$ is a [template](#templates) of the form - ``` + ```scala $sc$ with $mt_1$ with $\ldots$ with $mt_m$ { $\mathit{stats}$ } // $m \geq 0$ ``` @@ -768,12 +770,12 @@ class Sensitive private () { ### Constructor Definitions ```ebnf -FunDef ::= `this' ParamClause ParamClauses - (`=' ConstrExpr | [nl] ConstrBlock) +FunDef ::= ‘this’ ParamClause ParamClauses + (‘=’ ConstrExpr | [nl] ConstrBlock) ConstrExpr ::= SelfInvocation | ConstrBlock -ConstrBlock ::= `{' SelfInvocation {semi BlockStat} `}' -SelfInvocation ::= `this' ArgumentExprs {ArgumentExprs} +ConstrBlock ::= ‘{’ SelfInvocation {semi BlockStat} ‘}’ +SelfInvocation ::= ‘this’ ArgumentExprs {ArgumentExprs} ``` A class may have additional constructors besides the primary @@ -836,18 +838,19 @@ third one constructs a list with a given head and tail. ### Case Classes ```ebnf -TmplDef ::= `case' `class' ClassDef +TmplDef ::= ‘case’ ‘class’ ClassDef ``` If a class definition is prefixed with `case`, the class is said to be a _case class_. -The formal parameters in the first parameter section of a case class -are called _elements_; they are treated -specially. First, the value of such a parameter can be extracted as a +A case class is required to have a parameter section that is not implicit. +The formal parameters in the first parameter section +are called _elements_ and are treated specially. +First, the value of such a parameter can be extracted as a field of a constructor pattern. Second, a `val` prefix is -implicitly added to such a parameter, unless the parameter carries -already a `val` or `var` modifier. Hence, an accessor +implicitly added to such a parameter, unless the parameter already carries +a `val` or `var` modifier. Hence, an accessor definition for the parameter is [generated](#class-definitions). A case class definition of `$c$[$\mathit{tps}\,$]($\mathit{ps}_1\,$)$\ldots$($\mathit{ps}_n$)` with type @@ -965,12 +968,12 @@ directly extend `Expr` must be in the same source file as ## Traits ```ebnf -TmplDef ::= `trait' TraitDef +TmplDef ::= ‘trait’ TraitDef TraitDef ::= id [TypeParamClause] TraitTemplateOpt -TraitTemplateOpt ::= `extends' TraitTemplate | [[`extends'] TemplateBody] +TraitTemplateOpt ::= ‘extends’ TraitTemplate | [[‘extends’] TemplateBody] ``` -A trait is a class that is meant to be added to some other class +A _trait_ is a class that is meant to be added to some other class as a mixin. Unlike normal classes, traits cannot have constructor parameters. Furthermore, no constructor arguments are passed to the superclass of the trait. This is not necessary as traits are @@ -1072,7 +1075,7 @@ in `MyTable`. ObjectDef ::= id ClassTemplate ``` -An object definition defines a single object of a new class. Its +An _object definition_ defines a single object of a new class. Its most general form is `object $m$ extends $t$`. Here, $m$ is the name of the object to be defined, and @@ -1101,8 +1104,8 @@ Note that the value defined by an object definition is instantiated lazily. The `new $m$\$cls` constructor is evaluated not at the point of the object definition, but is instead evaluated the first time $m$ is dereferenced during execution of the program -(which might be never at all). An attempt to dereference $m$ again in -the course of evaluation of the constructor leads to a infinite loop +(which might be never at all). An attempt to dereference $m$ again +during evaluation of the constructor will lead to an infinite loop or run-time error. Other threads trying to dereference $m$ while the constructor is being evaluated block until evaluation is complete. |