There are various equality operators. ｢==｣ Tests for numeric equality ｢eq｣ Tests for string equality ｢===｣ Tests for value identity ｢=:=｣ Tests for pointer equality (Note that it looks a bit like ｢:=｣) ｢eqv｣ Tests for structure equivalence.
The ｢==｣ and ｢eq｣ operators are special because they force their values to be numbers or strings before they do anything else. There are similarly a variety of comparison operators. On Tue, May 26, 2020 at 5:06 PM ToddAndMargo via perl6-users < perl6-us...@perl.org> wrote: > >> On Tue, May 26, 2020 at 4:24 PM ToddAndMargo via perl6-users > >> <perl6-us...@perl.org <mailto:perl6-us...@perl.org>> wrote: > >> > >> Hi All, > >> > >> How do I turn this: > >> > >> $ raku -e 'my $x="abc"; say $x.index( "q" );' > >> Nil > >> > >> into a test? > >> > >> $ raku -e 'my $x="abc"; if $x.index( "q" ) eq Nil {say > "Nil"}else{say > >> "Exists";}' > >> Use of Nil in string context > >> in block <unit> at -e line 1 > >> Use of Nil in string context > >> in block <unit> at -e line 1 > >> Nil > >> > >> > >> Many thanks, > >> -T > >> > > On 2020-05-26 15:00, Brad Gilbert wrote: > > Generally you don't need to test for ｢Nil｣. > > You can just test for defined-ness. > > True enough > > > > > $ raku -e 'my $x="abc"; with $x.index( "q" ) {say "Exists"} else > > {say "Nil";}' > > > > Also ｢Nil｣ is not a ｢Str｣, so why would you use ｢eq｣? > > Because == did not work > > > > $ raku -e 'Nil.Str' > > Use of Nil in string context > > > > If you really need to check specifically for ｢Nil｣ (which you probably > > don't), then you can use ｢===｣. > > > > for Str, Int, Nil { > > say 'Nil' if $_ === Nil; > > } > > > > The ｢//｣ operator can also be useful to deal with undefined values such > > as ｢Nil｣. > > > > my $x = 'abc'; > > say $x.index('q') // 'cannot find the index of ｢q｣'; > > > > > > Hi Brad, > > Did not know about the triple = > > Thank you! > > -T > > > $ raku -e 'my $x="abc"; if $x.index( "q" ) === Nil {say "Nil"}else{say > "Exists";}' > Nil > > $ raku -e 'my $x="abc"; if $x.index( "a" ) === Nil {say "Nil"}else{say > "Exists";}' > Exists > > And I found buried in my Nil notes that `=:=` works too > > $ raku -e 'my $x="abc"; if $x.index( "q" ) =:= Nil {say "Nil"}else{say > "Exists";}' > Nil > > $ raku -e 'my $x="abc"; if $x.index( "b" ) =:= Nil {say "Nil"}else{say > "Exists";}' > Exists >
