It is possible to get current line number by __LINE__ in Ruby or Perl.
For example:
print "filename: #{__FILE__}, line: #{__LINE__}"
Is there the same feature in Groovy?
Not directly, but you can get it through an Exception (or Throwable) stack trace. For example:
StackTraceElement getStackFrame(String debugMethodName) {
def ignorePackages = [
'sun.',
'java.lang',
'org.codehaus',
'groovy.lang'
]
StackTraceElement frame = null
Throwable t = new Throwable()
t.stackTrace.eachWithIndex { StackTraceElement stElement, int index ->
if (stElement.methodName.contains(debugMethodName)) {
int callerIndex = index + 1
while (t.stackTrace[callerIndex].isNativeMethod() ||
ignorePackages.any { String packageName ->
t.stackTrace[callerIndex].className.startsWith(packageName)
}) {
callerIndex++
}
frame = t.stackTrace[callerIndex]
return
}
}
frame
}
int getLineNumber() {
getStackFrame('getLineNumber')?.lineNumber ?: -1
}
String getFileName() {
getStackFrame('getFileName')?.fileName
}
String getMethodName() {
getStackFrame('getMethodName')?.methodName
}
def foo() {
println "looking at $fileName:$lineNumber ($methodName)"
}
foo()
// ==> looking at test.groovy:39 (foo)
A word of caution though: getting the line number, file name, or method like this is very slow.
I'm not an expert in Groovy, but I don't think so. I know that Java and C# don't have it.
The __LINE__ feature really started to help with debugging in C. C doesn't have exceptions or many of the other features modern languages have, but it did have macros that the compiler could expand anywhere in the code, which is why we needed __FILE__, __LINE__, etc to let us know where we were when something bad happened. This is how assert works in C and C++. The JVM has very good debugging tools, and combined with assert and exceptions, you can very easily pinpoint where something went wrong (stack traces are way better than just a line number anyway).
I believe the reason Ruby and Perl have those macros is because they were created by C hackers. I've never used either of those languages enough to know the level of debugging support or how useful the macros really are.
Related
Kotlin deprecated the capitalize function on String class, and their suggested replacement is obnoxiously long. This is an example of a situation where they made the right call on deprecating it, but the wrong call on the user experience.
For example, this code:
val x = listOf("foo", "bar", "baz").map { it.capitalize() }
is "cleaned up" by the IDE to become:
val x = listOf("foo", "bar", "baz").map { it.replaceFirstChar {
if (it.isLowerCase()) it.titlecase(
Locale.getDefault()
) else it.toString()
} }
This is preeeeetty ugly. What can we do about it?
The suggested replacement is ugly because it needs to be equivalent to what capitalize() used to do:
dependent on the default locale
NOT converting an uppercase first char into titlecase (e.g.
capitalize does NOT transform a leading 'DŽ' into 'Dž' - both are single characters here, try to select them)
If you didn't care too much about this behaviour, you can use a simpler expression using an invariant locale and unconditionally titlecasing the first character even if uppercase:
val x = listOf("foo", "bar", "baz").map { it.replaceFirstChar(Char::titlecase) }
This means that if the first character is uppercase like 'DŽ', it will be transformed into the titlecase variant 'Dž' anyway, while the original code wouldn't touch it. This might actually be desirable.
One of the reasons capitalize() has been deprecated is because the behaviour of the method was unclear. For instance:
behaviour #2 is pretty weird
not capitalizing words in a sentence might be unexpected (C# would titlecase every space-separated word)
not lowercasing other characters of the words might be unexpected as well
If you want to keep the exact current behaviour on purpose, but make it more convenient to use, you can always roll your own extension function with a name that suits you ("capitalize(d)" might not give enough info to the unaware reader):
fun String.titlecaseFirstCharIfItIsLowercase() = replaceFirstChar {
if (it.isLowerCase()) it.titlecase(Locale.getDefault()) else it.toString()
}
Or for the version with invariant locale that titlecases the uppercase chars:
fun String.titlecaseFirstChar() = replaceFirstChar(Char::titlecase)
A neat solution is to define a new extension function on String, which hides the gory details with a cleaner name:
/**
* Replacement for Kotlin's deprecated `capitalize()` function.
*/
fun String.capitalized(): String {
return this.replaceFirstChar {
if (it.isLowerCase())
it.titlecase(Locale.getDefault())
else it.toString()
}
}
Now your old code can look like this:
val x = listOf("foo", "bar", "baz").map { it.capitalized() }
You'll need to define the extension function at the top level in some package that you can import easily. For example, if you have a kotlin file called my.package.KotlinUtils (KotlinUtils.kt), and you put the definition inside it like so:
package my.package
fun String.capitalized(): String {...}
Then you can import it in your other packages with:
import my.package.capitalized
val fruits = listOf("baNana", "avocAdo", "apPle", "kiwifRuit")
fruits
.filter { it.startsWith("a") }
.sortedBy { it }
.map { it.lowercase().replaceFirstChar(Char::uppercase) }
.forEach { println(it) }
Output:
Apple
Avocado
You can call the replaceFirstChar function on the original string and pass the transform function as input. The transform function takes the first character and converts it to an uppercase character using the uppercase() function.
val list = listOf("foo", "bar", "baz") .map {
it.replaceFirstChar { firstChar ->
firstChar.uppercase()
}
}
println("List - > $list")
Output
List - > [Foo, Bar, Baz]
How about this?
fun main() {
val x = listOf("foo", "bar", "baz").map { it[0].uppercase() + it.drop(1) }
println(x)
}
Output:
[Foo, Bar, Baz]
If you are not sure (maybe you receive Strings from an API) if the first letter is upper or lower case , you can use the below method;
var title = "myTitle"
title.replaceFirstChar {
if (it.isLowerCase()) it.titlecase(Locale.getDefault()) else
it.toString()
}
New title will be "MyTitle"
You can use this extension function to capitalize first characture of String
fun String.capitalize(): String {
return this.replaceFirstChar {
if (it.isLowerCase()) it.titlecase(Locale.getDefault())
else it.toString()
}
}
And call this method like
"abcd".capitalize()
I found a method trying to capitalize a string that came from the API and it apparently worked, found it in the Kotlin docs:
println("kotlin".replaceFirstChar { it.uppercase() }) // Kotlin
and use it like this in my code:
binding.textDescriptions.text = "${it.Year} - ${it.Type.replaceFirstChar {it.uppercase()}}"
I use enums but can't find good way to check eqauling.
enum Turn {
A(value:Int);
B(value:Int);
}
class Test {
static function main() {
var turn = Turn.A(100);
//I want to Check turn is Turn.A(any value) without using 'switch'.
if (turn == Turn.A) ...
}
}
Is there any good and simple way to checking?
You can use the .match() function:
if (turn.match(Turn.A(_)))
I haven't tested this, but it might be faster using Type class:
if (Type.enumConstructor(turn) == "A") ...
Because it is unsafe ("A" could be a typo), I suggest to use ExprTools:
import haxe.macro.ExprTools.*;
if (Type.enumConstructor(turn) == toString(macro A)) ...
There is another way, but I don't think it is faster :
if (Type.enumIndex(turn) == Type.enumIndex(A(0))) ...
And you might get condition evaluated to true for different enums:
enum Color { Red; }
if (Type.enumIndex(turn) == Type.enumIndex(Red)) ... // true
I'm writing a mini-console of sorts and I'm trying to figure out how to extract things from a link. For example, in PHP this is a request variable
so:
http://somelink.com/somephp.php?variable1=10&variable2=20
Then PHP figures out the url parameters and assigns them to a variable.
How would I parse something like this in Swift?
So, given the string I'd want to take: variable1=10 and variable2=20 etc, is there a simple way to do this? I tried googling around but didn't really know what I was searching for.
I have a really horrible hacky way of doing this but it's not really extendable.
You’d be wanting NSURLComponents:
import Foundation
let urlStr = "http://somelink.com/somephp.php?variable1=10&variable2=20"
let components = NSURLComponents(string: urlStr)
components?.queryItems?.first?.name // Optional("variable1")
components?.queryItems?.first?.value // Optional("10")
You might find it helpful to add a subscript operator for the query items:
extension NSURLComponents {
subscript(queryItemName: String) -> String? {
// of course, if you do this a lot,
// cache it in a dictionary instead
for item in self.queryItems ?? [] {
if item.name == queryItemName {
return item.value
}
}
return nil
}
}
if let components = NSURLComponents(string: urlStr) {
components["variable1"] ?? "No value"
}
In the following fragment, how can I distinguish the second invocation instance of my sub foo from the first?
while ($whatever) {
foo(); foo(); # foo() and foo() have the same caller package, file, and line
}
Something like a super-caller() that returned file, line and column would do the trick. I'd prefer not to use source filters.
Background, or, isn't this a bit of an XY Problem?
I have a convenience module, Local::Thread::Once, that exposes functionality like pthread_once/std::call_once in an OO-ish way and also as a subroutine attribute. These are easy enough, since there is a natural and unambiguous "once_control" or "once_flag" in either case.
However, there is additionally a procedural interface — once { ... } — that currently serializes based on the $filename and $line returned by caller. Something like this:
sub once(&) {
my $user_routine = shift;
my (undef, $file, $line) = caller;
my $once_control = get_a_shared_flag_just_for_this_invocation($file, $line);
lock($once_control);
if (! $once_control) { $once_control++; $user_routine->(); }
return;
}
That's not precisely how it works — the real one is more efficient — but the point, again, is that invocation is keyed off of the file and line of the caller. This works, except that it cannot distinguish two invocations on the same line.
while ($whatever) {
once { foo(); }
once { bar(); } # OK, foo() and bar() each called only once
once { baz(); }; once { buz(); }; # :( buz() not called, not even once
}
Note that the address of $user_routine cannot be used as an additional discriminant, since subs are copied from one ithread to another.
I can live with this problem as a documented limitation for a very contrived use case, but I'd prefer to fix it somehow.
Devel::Callsite was written precisely for this purpose.
I had to read this a couple of times before I understood what you are talking about. How about a "super caller" function like:
my #last_caller = ("","","",0);
sub super_caller {
my ($pkg,$file,$line) = caller(1 + shift);
if ($pkg eq $last_caller[0] &&
$file eq $last_caller[1] &&
$line eq $last_caller[2]) {
$last_caller[3]++;
} else {
#last_caller = ($pkg,$file,$line,1);
}
return #last_caller;
}
It's like caller but the 4th element is a count of how many times we've seen this exact package, file, and line in a row.
The optree is still so much black magic to me, but here are my observations:
in walking the optree of a code reference, you encounter one B::COP structure
The B::COP structure has file, line, and cop_seq properties (among others)
The cop_seq property is different for different subroutine definitions
Ass-u-me-ing these are true and not a horribly incomplete model of what is happening, you can use file, line, and cop_seq as a key, or maybe even just cop_seq. Here's a proof of concept:
use B;
sub once (&) {
my $code = shift;
my $key = get_cop_seq($code);
print "once called with code '$key'\n";
}
my $optreedata;
sub get_cop_seq {
my $code = shift;
$optreedata = "";
B::walkoptree( B::svref_2object($code)->ROOT, "find_cop_seq" );
return $optreedata;
}
sub B::OP::find_cop_seq {
my $op = shift;
if (ref $op eq 'B::COP') {
$optreedata .= sprintf "%s:%d:%d", $op->file, $op->line, $op->cop_seq;
}
}
sub foo { 42 }
sub bar { 19 };
once { foo }; # this is line 26
once { bar };
once { foo }; once { bar };
once { bar } for 1..5; # line 29
And here's the output (your results may vary):
once called with code 'super-caller2.pl:26:205'
once called with code 'super-caller2.pl:27:206'
once called with code 'super-caller2.pl:28:207' <--- two calls for line 28
once called with code 'super-caller2.pl:28:208' |- with different cop_seq
once called with code 'super-caller2.pl:29:209'
once called with code 'super-caller2.pl:29:209'
once called with code 'super-caller2.pl:29:209' <--- but 5 calls for line 29
once called with code 'super-caller2.pl:29:209' with the same cop_seq
once called with code 'super-caller2.pl:29:209'
I would like to return from a closure, like one would if using a break statement in a loop.
For example:
largeListOfElements.each{ element->
if(element == specificElement){
// do some work
return // but this will only leave this iteration and start the next
}
}
In the above if statement I would like to stop iterating through the list and leave the closure to avoid unnecessary iterations.
I've seen a solution where an exception is thrown within the closure and caught outside, but I'm not too fond of that solution.
Are there any solutions to this, other than changing the code to avoid this kind of algorithm?
I think you want to use find instead of each (at least for the specified example). Closures don't directly support break.
Under the covers, groovy doesn't actually use a closure either for find, it uses a for loop.
Alternatively, you could write your own enhanced version of find/each iterator that takes a conditional test closure, and another closure to call if a match is found, having it break if a match is met.
Here's an example:
Object.metaClass.eachBreak = { ifClosure, workClosure ->
for (Iterator iter = delegate.iterator(); iter.hasNext();) {
def value = iter.next()
if (ifClosure.call(value)) {
workClosure.call(value)
break
}
}
}
def a = ["foo", "bar", "baz", "qux"]
a.eachBreak( { it.startsWith("b") } ) {
println "working on $it"
}
// prints "working on bar"
I think you're working on the wrong level of abstraction. The .each block does exactly what it says: it executes the closure once for each element. What you probably want instead is to use List.indexOf to find the right specificElement, and then do the work you need to do on it.
If you want to process all elements until a specific one was found you could also do something like this:
largeListOfElements.find { element ->
// do some work
element == specificElement
}
Although you can use this with any kind of "break condition".
I just used this to process the first n elements of a collection by returning
counter++ >= n
at the end of the closure.
As I understand groovy, the way to shortcut these kinds of loops would be to throw a user-defined exception. I don't know what the syntax would be (not a grrovy programmer), but groovy runs on the JVM so it would be something something like:
class ThisOne extends Exception {Object foo; ThisOne(Object foo) {this.foo=foo;}}
try { x.each{ if(it.isOk()) throw new ThisOne(it); false} }
catch(ThisOne x) { print x.foo + " is ok"; }
After paulmurray's answer I wasn't sure myself what would happen with an Exception thrown from within a closure, so I whipped up a JUnit Test Case that is easy to think about:
class TestCaseForThrowingExceptionFromInsideClosure {
#Test
void testEearlyReturnViaException() {
try {
[ 'a', 'b', 'c', 'd' ].each {
System.out.println(it)
if (it == 'c') {
throw new Exception("Found c")
}
}
}
catch (Exception exe) {
System.out.println(exe.message)
}
}
}
The output of the above is:
a
b
c
Found c
But remember that "one should NOT use Exceptions for flow control", see in particular this Stack Overflow question: Why not use exceptions as regular flow of control?
So the above solution is less than ideal in any case. Just use:
class TestCaseForThrowingExceptionFromInsideClosure {
#Test
void testEarlyReturnViaFind() {
def curSolution
[ 'a', 'b', 'c', 'd' ].find {
System.out.println(it)
curSolution = it
return (it == 'c') // if true is returned, find() stops
}
System.out.println("Found ${curSolution}")
}
}
The output of the above is also:
a
b
c
Found c
Today I faced a similar problem while working with each closure. I wanted to break the flow of execution based on my condition but couldn't do it.
The easiest way to do in groovy is to use any() on a list instead of each if you wish to return a boolean based on some condition.
Good ole for loop still works in Groovy for your use case
for (element in largeListOfElements) {
if(element == specificElement){
// do some work
return
}
}