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doc: document x := ?int(none)

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Alexander Medvednikov 2024-05-20 21:47:50 +03:00
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@ -2066,7 +2066,7 @@ from `low` up to *but not including* `high`.
> This exclusive range notation and zero-based indexing follow principles of > This exclusive range notation and zero-based indexing follow principles of
logical consistency and error reduction. As Edsger W. Dijkstra outlines in logical consistency and error reduction. As Edsger W. Dijkstra outlines in
'Why Numbering Should Start at Zero' 'Why Numbering Should Start at Zero'
([EWD831](https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html)), ([EWD831](https://www.cs.utexas.edu/users/EWD/transcriptions/EWD08xx/EWD831.html)),
zero-based indexing aligns the index with the preceding elements in a sequence, zero-based indexing aligns the index with the preceding elements in a sequence,
simplifying handling and minimizing errors, especially with adjacent subsequences. simplifying handling and minimizing errors, especially with adjacent subsequences.
This logical and efficient approach shapes our language design, emphasizing clarity This logical and efficient approach shapes our language design, emphasizing clarity
@ -3973,6 +3973,11 @@ fn main() {
println(user.name) // "Charles" println(user.name) // "Charles"
user2 := repo.find_user_by_id2(10) or { return } user2 := repo.find_user_by_id2(10) or { return }
// To create an Option var directly:
my_optional_int := ?int(none)
my_optional_string := ?string(none)
my_optional_user := ?User(none)
} }
``` ```
@ -6224,7 +6229,7 @@ See also [Cross Compilation](#cross-compilation).
## Debugger ## Debugger
To use the native *V debugger*, add the `$dbg` statement to your source, where you To use the native *V debugger*, add the `$dbg` statement to your source, where you
want the debugger to be invoked. want the debugger to be invoked.
```v ```v
@ -6234,18 +6239,18 @@ fn main() {
} }
``` ```
Running this V code, you will get the debugger REPL break when the execution Running this V code, you will get the debugger REPL break when the execution
reaches the `$dbg` statement. reaches the `$dbg` statement.
``` ```
$ v run example.v $ v run example.v
Break on [main] main in example.v:3 Break on [main] main in example.v:3
example.v:3 vdbg> example.v:3 vdbg>
``` ```
At this point, execution is halted, and the debugger is now available. At this point, execution is halted, and the debugger is now available.
To see the available commands, type To see the available commands, type
?, h or help. (Completion for commands works - Non-Windows only) ?, h or help. (Completion for commands works - Non-Windows only)
``` ```
@ -6311,7 +6316,7 @@ example.v:3 vdbg> l
0005 } 0005 }
``` ```
The default is read 3 lines before and 3 lines after, but you can The default is read 3 lines before and 3 lines after, but you can
pass a parameter to the command to read more lines, like `l 5`. pass a parameter to the command to read more lines, like `l 5`.
Now, lets watch the variable changing on this loop. Now, lets watch the variable changing on this loop.
@ -6331,21 +6336,21 @@ i = 1 (int)
`i` and it's value is automatically printed, because it is in the watch list. `i` and it's value is automatically printed, because it is in the watch list.
To repeat the last command issued, in this case the `c` command, To repeat the last command issued, in this case the `c` command,
just hit the *enter* key. just hit the *enter* key.
``` ```
example.v:3 vdbg> example.v:3 vdbg>
Break on [main] main in example.v:3 Break on [main] main in example.v:3
i = 2 (int) i = 2 (int)
example.v:3 vdbg> example.v:3 vdbg>
Break on [main] main in example.v:3 Break on [main] main in example.v:3
i = 3 (int) i = 3 (int)
example.v:3 vdbg> example.v:3 vdbg>
``` ```
You can also see memory usage with `mem` or `memory` command, and You can also see memory usage with `mem` or `memory` command, and
check if the current context is an anon function (`anon?`), a method (`method?`) check if the current context is an anon function (`anon?`), a method (`method?`)
or a generic method (`generic?`) and clear the terminal window (`clear`). or a generic method (`generic?`) and clear the terminal window (`clear`).
## Call stack ## Call stack
@ -6387,7 +6392,7 @@ example.v:5 | > main.test
## Trace ## Trace
Another feature of `v.debug` is the possibility to add hook functions Another feature of `v.debug` is the possibility to add hook functions
before and after each function call. before and after each function call.
To enable this feature, add the `-d trace` switch when building or running To enable this feature, add the `-d trace` switch when building or running
@ -7714,4 +7719,4 @@ Assignment Operators
+= -= *= /= %= += -= *= /= %=
&= |= ^= &= |= ^=
>>= <<= >>>= >>= <<= >>>=
``` ```