1 USING: classes classes.private help.markup help.syntax kernel
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5 ARTICLE: "class-operations" "Class operations"
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6 "Set-theoretic operations on classes:"
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17 ARTICLE: "class-linearization" "Class linearization"
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18 "Classes have an intrinsic partial order; given two classes A and B, we either have that A is a subset of B, B is a subset of A, A and B are equal as sets, or they are incomparable. The last two situations present difficulties for method dispatch:"
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20 "If a generic word defines a method on a mixin class A and another on class B, and B is the only instance of A, there is an ambiguity because A and B are equal as sets; any object that is an instance of one is an instance of both."
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21 { "If a generic word defines methods on two union classes which are incomparable but not disjoint, for example " { $link sequence } " and " { $link number } ", there is an ambiguity because the generic word may be called on an object that is an instance of both unions." }
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23 "The first ambiguity is resolved with a tie-breaker that compares metaclasses. The intrinsic meta-class order, from most-specific to least-specific:"
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25 "Built-in classes and tuple classes"
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30 "This means that in the above example, the generic word with methods on a mixin and its sole instance will always call the method for the sole instance, since it is more specific than a mixin class."
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32 "The second problem is resolved with another tie-breaker. When performing the topological sort of classes, if there are multiple candidates at any given step of the sort, lexicographical order on the class name is used."
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41 { $subsections rank-class } ;
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44 { $values { "class" class } { "assoc" "an assoc whose keys are classes" } }
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45 { $description "Outputs a set of builtin and tuple classes whose union is the smallest cover of " { $snippet "class" } "." } ;
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48 { $values { "first" "a class" } { "second" "a class" } { "?" boolean } }
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49 { $description "Tests if all instances of " { $snippet "class1" } " are also instances of " { $snippet "class2" } "." }
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50 { $notes "Classes are partially ordered. This means that if " { $snippet "class1 <= class2" } " and " { $snippet "class2 <= class1" } ", then " { $snippet "class1 <= class2" } ". Also, if " { $snippet "class1 <= class2" } " and " { $snippet "class2 <= class3" } ", then " { $snippet "class1 <= class3" } "." } ;
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53 { $values { "seq" "a sequence of class" } { "newseq" "a new sequence of classes" } }
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54 { $description "Outputs a linear sort of a sequence of classes. Larger classes come before their subclasses." } ;
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57 { $values { "first" class } { "second" class } { "class" class } }
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58 { $description "Outputs the smallest anonymous class containing both " { $snippet "class1" } " and " { $snippet "class2" } "." } ;
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61 { $values { "first" class } { "second" class } { "class" class } }
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62 { $description "Outputs the largest anonymous class contained in both " { $snippet "class1" } " and " { $snippet "class2" } "." } ;
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64 HELP: classes-intersect?
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65 { $values { "first" class } { "second" class } { "?" boolean } }
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66 { $description "Tests if two classes have a non-empty intersection. If the intersection is empty, no object can be an instance of both classes at once." } ;
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68 HELP: smallest-class
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69 { $values { "classes" "a sequence of class words" } { "class/f" { $maybe class } } }
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70 { $description "Outputs a minimum class from the given sequence." } ;
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