I have just started learning Groovy which looks really awesome!
This is very simple example.
"Groovy".each {a -> println a};
It nicely prints as given below.
G
r
o
o
v
y
My question is - 'each' method is not part of String object as per the link below. Then how come it works?
http://beta.groovy-lang.org/docs/latest/html/groovy-jdk/
How can i get the parameters list for a closure of an object?
example String.each has 1 parameter, Map.each has 1 or 2 parameters like entry or key & value.
The relevant code in DefaultGroovyMethods is
public static Iterator iterator(Object o) {
return DefaultTypeTransformation.asCollection(o).iterator();
}
which contains:
else if (value instanceof String) {
return StringGroovyMethods.toList((String) value);
}
String toList is:
public static List<String> toList(String self) {
int size = self.length();
List<String> answer = new ArrayList<String>(size);
for (int i = 0; i < size; i++) {
answer.add(self.substring(i, i + 1));
}
return answer;
}
Related
I'm trying to multiply some string a by some integer b such that a * b = a + a + a... (b times). I've tried doing it the same way I would in python:
class Test {
static function main() {
var a = "Text";
var b = 4;
trace(a * b); //Assumed Output: TextTextTextText
}
}
But this raises:
Build failure Test.hx:6: characters 14-15 : String should be Int
There doesn't seem to be any information in the Haxe Programming Cookbook or the API Documentation about multiplying strings, so I'm wondering if I've mistyped something or if I should use:
class Test {
static function main() {
var a = "Text";
var b = 4;
var c = "";
for (i in 0...b) {
c = c + a;
}
trace(c); // Outputs "TextTextTextText"
}
}
Not very short, but array comprehension might help in some situations :
class Test {
static function main() {
var a = "Text";
var b = 4;
trace( [for (i in 0...b) a].join("") );
//Output: TextTextTextText
}
}
See on try.haxe.org.
The numeric multiplication operator * requires numeric types, like integer. You have a string. If you want to multiply a string, you have to do it manually by appending a target string within the loop.
The + operator is not the numeric plus in your example, but a way to combine strings.
You can achieve what you want by operator overloading:
abstract MyAbstract(String) {
public inline function new(s:String) {
this = s;
}
#:op(A * B)
public function repeat(rhs:Int):MyAbstract {
var s:StringBuf = new StringBuf();
for (i in 0...rhs)
s.add(this);
return new MyAbstract(s.toString());
}
}
class Main {
static public function main() {
var a = new MyAbstract("foo");
trace(a * 3); // foofoofoo
}
}
To build on tokiop's answer, you could also define a times function, and then use it as a static extension.
using Test.Extensions;
class Test {
static function main() {
trace ("Text".times(4));
}
}
class Extensions {
public static function times (str:String, n:Int) {
return [for (i in 0...n) str].join("");
}
}
try.haxe.org demo here
To build on bsinky answer, you can also define a times function as static extension, but avoid the array:
using Test.Extensions;
class Test {
static function main() {
trace ("Text".times(4));
}
}
class Extensions {
public static function times (str:String, n:Int) {
var v = new StringBuf();
for (i in 0...n) v.add(str);
return v.toString();
}
}
Demo: https://try.haxe.org/#e5937
StringBuf may be optimized for different targets. For example, on JavaScript target it is compiled as if you were just using strings https://api.haxe.org/StringBuf.html
The fastest method (at least on the JavaScript target from https://try.haxe.org/#195A8) seems to be using StringTools._pad.
public static inline function stringProduct ( s : String, n : Int ) {
if ( n < 0 ) {
throw ( 1 );
}
return StringTools.lpad ( "", s, s.length * n );
}
StringTools.lpad and StringTools.rpad can't seem to decide which is more efficient. It looks like rpad might be better for larger strings and lpad might be better for smaller strings, but they switch around a bit with each rerun. haxe.format.JsonPrinter uses lpad for concatenation, but I'm not sure which to recommend.
I recently started to learn Groovy and found not a natural behavior.
class BasicRouter {
int method_(first){
return 1;
}
int method_(int first){
return 2;
}
int method_(short second){
return 3;
}
int method_(Integer first){
return 4;
}
}
br = new BasicRouter()
int x = 1
assert br.method_(x) == 4
assert br.method_((int)29) == 2
Why in the first case we are passing a variable of type int, we get 4 and not 2?
I expect that method int method_(int) will be called.
Thanks.
The answer is here - http://docs.groovy-lang.org/latest/html/documentation/core-differences-java.html#_primitives_and_wrappers
Groovy uses objects for everything
This changes if you use CompileStatic
#groovy.transform.CompileStatic
def fInt(int x) {new BasicRouter().method_(x)}
assert fInt(1) == 2
I have class in groovy
class WhsDBFile {
String name
String path
String svnUrl
String lastRevision
String lastMessage
String lastAuthor
}
and map object
def installFiles = [:]
that filled in loop by
WhsDBFile dbFile = new WhsDBFile()
installFiles[svnDiffStatus.getPath()] = dbFile
now i try to sort this with custom Comparator
Comparator<WhsDBFile> whsDBFileComparator = new Comparator<WhsDBFile>() {
#Override
int compare(WhsDBFile o1, WhsDBFile o2) {
if (FilenameUtils.getBaseName(o1.name) > FilenameUtils.getBaseName(o2.name)) {
return 1
} else if (FilenameUtils.getBaseName(o1.name) > FilenameUtils.getBaseName(o2.name)) {
return -1
}
return 0
}
}
installFiles.sort(whsDBFileComparator);
but get this error java.lang.String cannot be cast to WhsDBFile
Any idea how to fix this? I need to use custom comparator, cause it will be much more complex in the future.
p.s. full source of sample gradle task (description of WhsDBFile class is above):
project.task('sample') << {
def installFiles = [:]
WhsDBFile dbFile = new WhsDBFile()
installFiles['sample_path'] = dbFile
Comparator<WhsDBFile> whsDBFileComparator = new Comparator<WhsDBFile>() {
#Override
int compare(WhsDBFile o1, WhsDBFile o2) {
if (o1.name > o2.name) {
return 1
} else if (o1.name > o2.name) {
return -1
}
return 0
}
}
installFiles.sort(whsDBFileComparator);
}
You can try to sort the entrySet() :
def sortedEntries = installFiles.entrySet().sort { entry1, entry2 ->
entry1.value <=> entry2.value
}
you will have a collection of Map.Entry with this invocation. In order to have a map, you can then collectEntries() the result :
def sortedMap = installFiles.entrySet().sort { entry1, entry2 ->
...
}.collectEntries()
sort can also take a closure as parameter which coerces to a Comparator's compare() method as below. Usage of toUpper() method just mimics the implementation of FilenameUtils.getBaseName().
installFiles.sort { a, b ->
toUpper(a.value.name) <=> toUpper(b.value.name)
}
// Replicating implementation of FilenameUtils.getBaseName()
// This can be customized according to requirement
String toUpper(String a) {
a.toUpperCase()
}
I want to implement Maybe from Haskell in D, just for the hell of it.
This is what I've got so far, but it's not that great. Any ideas how to improve it?
class Maybe(a = int){ } //problem 1: works only with ints
class Just(alias a) : Maybe!(typeof(a)){ }
class Nothing : Maybe!(){ }
Maybe!int doSomething(in int k){
if(k < 10)
return new Just!3; //problem 2: can't say 'Just!k'
else
return new Nothing;
}
Haskell Maybe definition:
data Maybe a = Nothing | Just a
what if you use this
class Maybe(T){ }
class Just(T) : Maybe!(T){
T t;
this(T t){
this.t = t;
}
}
class Nothing : Maybe!(){ }
Maybe!int doSomething(in int k){
if(k < 10)
return new Just!int(3);
else
return new Nothing;
}
personally I'd use tagged union and structs though (and enforce it's a Just when getting the value)
Look at std.typecons.Nullable. It's not exactly the same as Maybe in Haskell, but it's a type which optionally holds a value of whatever type it's instantiated with. So, effectively, it's like Haskell's Maybe, though syntactically, it's a bit different. The source is here if you want to look at it.
I haven't used the Maybe library, but something like this seems to fit the bill:
import std.stdio;
struct Maybe(T)
{
private {
bool isNothing = true;
T value;
}
void opAssign(T val)
{
isNothing = false;
value = val;
}
void opAssign(Maybe!T val)
{
isNothing = val.isNothing;
value = val.value;
}
T get() #property
{
if (!isNothing)
return value;
else
throw new Exception("This is nothing!");
}
bool hasValue() #property
{
return !isNothing;
}
}
Maybe!int doSomething(in int k)
{
Maybe!int ret;
if (k < 10)
ret = 3;
return ret;
}
void main()
{
auto retVal = doSomething(5);
assert(retVal.hasValue);
writeln(retVal.get);
retVal = doSomething(15);
assert(!retVal.hasValue);
writeln(retVal.hasValue);
}
With some creative operator overloading, the Maybe struct could behave quite naturally. Additionally, I've templated the Maybe struct, so it can be used with any type.
I'm creating an object at runtime using reflection emit. I successfully created the fields, properties and get set methods.
Now I want to add a method. For the sake of simplicity let's say the method just returns a random number. How do I define the method body?
EDIT:
Yes, I've been looking at the msdn documentation along with other references and I'm starting to get my head wrapped around this stuff.
I see how the example above is adding and/or multplying, but what if my method is doing other stuff. How do I define that "stuff"
Suppose I was generating the class below dynamically, how would I create the body of GetDetails() method?
class TestClass
{
public string Name { get; set; }
public int Size { get; set; }
public TestClass()
{
}
public TestClass(string Name, int Size)
{
this.Name = Name;
this.Size = Size;
}
public string GetDetails()
{
string Details = "Name = " + this.Name + ", Size = " + this.Size.ToString();
return Details;
}
}
You use a MethodBuilder to define methods. To define the method body, you call GetILGenerator() to get an ILGenerator, and then call the Emit methods to emit individual IL instructions. There is an example on the MSDN documentation for MethodBuilder, and you can find other examples of how to use reflection emit on the Using Reflection Emit page:
public static void AddMethodDynamically(TypeBuilder myTypeBld,
string mthdName,
Type[] mthdParams,
Type returnType,
string mthdAction)
{
MethodBuilder myMthdBld = myTypeBld.DefineMethod(
mthdName,
MethodAttributes.Public |
MethodAttributes.Static,
returnType,
mthdParams);
ILGenerator ILout = myMthdBld.GetILGenerator();
int numParams = mthdParams.Length;
for (byte x = 0; x < numParams; x++)
{
ILout.Emit(OpCodes.Ldarg_S, x);
}
if (numParams > 1)
{
for (int y = 0; y < (numParams - 1); y++)
{
switch (mthdAction)
{
case "A": ILout.Emit(OpCodes.Add);
break;
case "M": ILout.Emit(OpCodes.Mul);
break;
default: ILout.Emit(OpCodes.Add);
break;
}
}
}
ILout.Emit(OpCodes.Ret);
}
It sounds like you're looking for resources on writing MSIL. One important resource is the OpCodes class, which has a member for every IL instruction. The documentation describes how each instruction works. Another important resource is either Ildasm or Reflector. These will let you see the IL for compiled code, which will help you understand what IL you want to write. Running your GetDetailsMethod through Reflector and setting the language to IL yields:
.method public hidebysig instance string GetDetails() cil managed
{
.maxstack 4
.locals init (
[0] string Details,
[1] string CS$1$0000,
[2] int32 CS$0$0001)
L_0000: nop
L_0001: ldstr "Name = "
L_0006: ldarg.0
L_0007: call instance string ConsoleApplication1.TestClass::get_Name()
L_000c: ldstr ", Size = "
L_0011: ldarg.0
L_0012: call instance int32 ConsoleApplication1.TestClass::get_Size()
L_0017: stloc.2
L_0018: ldloca.s CS$0$0001
L_001a: call instance string [mscorlib]System.Int32::ToString()
L_001f: call string [mscorlib]System.String::Concat(string, string, string, string)
L_0024: stloc.0
L_0025: ldloc.0
L_0026: stloc.1
L_0027: br.s L_0029
L_0029: ldloc.1
L_002a: ret
}
To generate a method like that dynamically, you will need to call ILGenerator.Emit for each instruction:
ilGen.Emit(OpCodes.Nop);
ilGen.Emit(OpCodes.Ldstr, "Name = ");
ilGen.Emit(OpCodes.Ldarg_0);
ilGen.Emit(OpCodes.Call, nameProperty.GetGetMethod());
// etc..
You may also want to look for introductions to MSIL, such as this one: Introduction to IL Assembly Language.