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diff --git a/doc/hash_inclusion.rdoc b/doc/hash_inclusion.rdoc new file mode 100644 index 0000000000..05c2b0932a --- /dev/null +++ b/doc/hash_inclusion.rdoc @@ -0,0 +1,31 @@ +== \Hash Inclusion + +A hash is set-like in that it cannot have duplicate entries +(or even duplicate keys). +\Hash inclusion can therefore based on the idea of +{subset and superset}[https://en.wikipedia.org/wiki/Subset]. + +Two hashes may be tested for inclusion, +based on comparisons of their entries. + +An entry <tt>h0[k0]</tt> in one hash +is equal to an entry <tt>h1[k1]</tt> in another hash +if and only if the two keys are equal (<tt>k0 == k1</tt>) +and their two values are equal (<tt>h0[k0] == h1[h1]</tt>). + +A hash may be a subset or a superset of another hash: + +- Subset (included in or equal to another): + + - \Hash +h0+ is a _subset_ of hash +h1+ (see Hash#<=) + if each entry in +h0+ is equal to an entry in +h1+. + - Further, +h0+ is a <i>proper subset</i> of +h1+ (see Hash#<) + if +h1+ is larger than +h0+. + +- Superset (including or equal to another): + + - \Hash +h0+ is a _superset_ of hash +h1+ (see Hash#>=) + if each entry in +h1+ is equal to an entry in +h0+. + - Further, +h0+ is a <i>proper superset</i> of +h1+ (see Hash#>) + if +h0+ is larger than +h1+. + |