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This channel is intended for people just starting with the Raku Programming Language (raku.org). Logs are available at irclogs.raku.org/raku-beginner/live.html Set by lizmat on 8 June 2022. |
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| deoac | In a `class` , what's the difference between `state $i` and `our $i` ? | 18:28 | |
| librasteve | a class is just a fancy block | 19:17 | |
| my scope lexical variables are available in the block and in any enclosed blocks | 19:18 | ||
| our scope package variables are available anywhere in the package and not limited to the block ... this is generally bad since you lose locality | 19:19 | ||
| my scope variables are re-declared each time their block is entered - so generally they are different in each pass (for example in recursive code, each call to the block has a new set of my variables) | 19:21 | ||
| state scope variables are local to the block, but they are only initialized once, so state variables will retain their value across multiple executions of the enclosing block or routine | 19:24 | ||
| so you can use them for things like count how many times a block is executed | 19:25 | ||
| in a class this means you can use a class state variable to count (or limit) the number of instance | |||
| Nemokosch | a class itself is a package, let's not forget that | ||
| deoac | I can also use an our variable to count how many times the class in initiated. | 19:32 | |
| librasteve | m: class A { state $s; method s { $s += 1 } } my $a1 = A.new; say $a1.s; my $a2 = A.new; say $a2.s; | 19:35 | |
| Raku eval | Exit code: 1 ===SORRY!=== Error while compiling /home/glot/main.raku Strange text after block (missing semicolon or comma?) at /home/glot/main.raku:1 ------> ass A { state $s; method s { $s += 1 } }⏏ my $a1 = A.new; say $a1.s; my $a2 = A.n expecting any of: infix infix stopper statement end statement modifier statement modifier loop | ||
| librasteve | m: class A { state $s; method s { $s += 1 } }; my $a1 = A.new; say $a1.s; my $a2 = A.new; say $a2.s; | ||
| Raku eval | 1 2 | 19:36 | |
| librasteve | m: class B { our $o; method o { $o += 1 } }; my $b1 = B.new; say $b1.o; my $b2 = B.new; say $b2.o; | ||
| Raku eval | 1 2 | ||
| librasteve | I had not appreciated that class is a package, so both our and state are available to all instances (ie class variables) | 19:37 | |
| m: class A { state $s; method s { $s += 1 } }; my $a1 = A.new; say $a1.s; say $A::s; | 19:46 | ||
| Raku eval | 1 (Any) | ||
| librasteve | ^^^ state variables (like my vars) are fully private | 19:47 | |
| m: class B { our $o; method o { $o += 1 } }; my $b1 = B.new; say $b1.o; say $B::o; | |||
| Raku eval | 1 1 | ||
| librasteve | ^^^ you can access the our variable (eg from another class) via the fully qualified name (fqn) | 19:48 | |
| I guess you already saw the Class Variables doc docs.raku.org/language/classtut#Class_variables | |||
| looking at these examples, the class block is only initialized once so there is no special behaviour of state vs my afaict since the magic of state is that it is only initialized once when the block is executed multiple times | 19:56 | ||
| deoac | Is this summation accurate? gist.github.com/deoac/784de6ec9b5a...e89d2.html | 20:06 | |
| librasteve | there is a small point 'my class A' is fine but 'class A' does the same thing since class is default 'my scoped' | 21:04 | |
| otherwise, at a quick look it is right and I see that you have added TWEAK as the point to do the increment which looks good | 21:05 | ||
| BUT --- I think that your code example clarifies that (i) using state scope for a class variable is useless (and thus may be confusing to the reader) since the class block is only executed once and (ii) there is only a very fine distinction between my scope and our scope in that our scope is slightly leaky since you can use FQN and, unlike my is not strictly private | 21:09 | ||
| oh - I think that there is an error in your gist in that dd $B::count should give you the value | 21:11 | ||
| ^^ no your gist is right, and it also shows that inheritance via 'is' does not clone the FQNs to the child class name ... which seems fine to me as default behaviour | 21:22 | ||
| deoac | Thanks for all this help. Can you give me an example where a state variable would behave differently from an our variable? | 21:32 | |
| avuserow | m: sub foo {state $s = 0; $s++; say $s}; foo() for ^5 | 22:43 | |
| camelia | 1 2 3 4 5 |
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| avuserow | m: sub foo {our $s = 0; $s++; say $s}; foo() for ^5 | ||
| camelia | 1 1 1 1 1 |
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| avuserow | m: {my $s = 0; sub foo {$s++; say $s}}; foo() for ^5 # approximation of `state` using another block | 22:44 | |
| camelia | ===SORRY!=== Error while compiling <tmp> Undeclared routine: foo used at line 1 |
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| avuserow | m: {my $s = 0; our sub foo {$s++; say $s}}; foo() for ^5 # approximation of `state` using another block | ||
| camelia | ===SORRY!=== Error while compiling <tmp> Undeclared routine: foo used at line 1 |
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| avuserow | m: my &foo = do {my $s = 0; sub {$s++; say $s}}; foo() for ^5 # approximation of `state` using another block | 22:48 | |
| camelia | 1 2 3 4 5 |
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