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  • bug with varargs and overloading?

    - by pstanton
    There seems to be a bug in the Java varargs implementation. Java can't distinguish the appropriate type when a method is overloaded with different types of vararg parameters. It gives me an error The method ... is ambiguous for the type ... Consider the following code: public class Test { public static void main(String[] args) throws Throwable { doit(new int[]{1, 2}); // <- no problem doit(new double[]{1.2, 2.2}); // <- no problem doit(1.2f, 2.2f); // <- no problem doit(1.2d, 2.2d); // <- no problem doit(1, 2); // <- The method doit(double[]) is ambiguous for the type Test } public static void doit(double... ds) { System.out.println("doubles"); } public static void doit(int... is) { System.out.println("ints"); } } the docs say: "Generally speaking, you should not overload a varargs method, or it will be difficult for programmers to figure out which overloading gets called." however they don't mention this error, and it's not the programmers that are finding it difficult, it's the compiler. thoughts?

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  • toString method for varargs contructor

    - by owca
    I have a varargs contructor like this : public class Sentence { public String[] str; public Sentence(Object... text){ StringBuilder sb = new StringBuilder(); for (Object o : text) { sb.append(o.toString()) .append(" "); } System.out.println(sb.toString()); } } Contructor can get various types of data (ints, strings, and Sentence objects as well). How to do a proper toString method for such class ?

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  • How to properly match varargs in Mockito

    - by qualidafial
    I've been trying to get to mock a method with vararg parameters using Mockito: interface A { B b(int x, int y, C... c); } A a = mock(A.class); B b = mock(B.class); when(a.b(anyInt(), anyInt(), any(C[].class))).thenReturn(b); assertEquals(b, a.b(1, 2)); This doesn't work, however if I do this instead: when(a.b(anyInt(), anyInt())).thenReturn(b); assertEquals(b, a.b(1, 2)); This works, despite that I have completely omitted the varargs argument when stubbing the method. Any clues?

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  • Combine guava's ImmutableList and varargs

    - by Stas Kurilin
    I want create constructor that will take one or more integers and save it into field as ImmutableList. According to "The right way to use varargs to pass one or more arguments" by Bloch's Item 42 I create smt like class Foo{ private final ImmutableList<Integer> bar; public Foo(Integer first, Integer... other) { this.bar = ImmutableList.<Integer>builder() .add(first) .addAll(Arrays.asList(other)) .build(); } } Why builder doesn't get generic automatically? And, as it smells. How I can rewrite it?

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  • Are there gotchas using varargs with reference parameters

    - by Roddy
    I have this piece of code (summarized)... AnsiString working(AnsiString format,...) { va_list argptr; AnsiString buff; va_start(argptr, format); buff.vprintf(format.c_str(), argptr); va_end(argptr); return buff; } And, on the basis that pass by reference is preferred where possible, I changed it thusly. AnsiString broken(const AnsiString &format,...) { ... the rest, totally identical ... } My calling code is like this:- AnsiString s1, s2; s1 = working("Hello %s", "World"); s2 = broken("Hello %s", "World"); But, s1 contains "Hello World", while s2 has "Hello (null)". I think this is due to the way va_start works, but I'm not exactly sure what's going on.

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  • How to work with varargs and reflection

    - by PeterMmm
    Simple question, how make this code working ? public class T { public static void main(String[] args) throws Exception { new T().m(); } public // as mentioned by Bozho void foo(String... s) { System.err.println(s[0]); } void m() throws Exception { String[] a = new String[]{"hello", "kitty"}; System.err.println(a.getClass()); Method m = getClass().getMethod("foo", a.getClass()); m.invoke(this, (Object[]) a); } } Output: class [Ljava.lang.String; Exception in thread "main" java.lang.IllegalArgumentException: wrong number of arguments at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597)

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  • Looping through macro Varargs values

    - by Ed Marty
    If I define some macro: #define foo(args...) ({/*do something*/}) Is there some way to actually loop through args rather than pass it along to another function? Something like #define foo(args...) \ { \ for (int i = 0; i < sizeof(args); ++i) { \ /*do something with args[i]*/ \ } \ }

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  • varargs in lambda functions in Python

    - by brain_damage
    Is it possible a lambda function to have variable number of arguments? For example, I want to write a metaclass, which creates a method for every method of some other class and this newly created method returns the opposite value of the original method and has the same number of arguments. And I want to do this with lambda function. How to pass the arguments? Is it possible? class Negate(type): def __new__(mcs, name, bases, _dict): extended_dict = _dict.copy() for (k, v) in _dict.items(): if hasattr(v, '__call__'): extended_dict["not_" + k] = lambda s, *args, **kw: not v(s, *args, **kw) return type.__new__(mcs, name, bases, extended_dict) class P(metaclass=Negate): def __init__(self, a): self.a = a def yes(self): return True def maybe(self, you_can_chose): return you_can_chose But the result is totally wrong: >>>p = P(0) >>>p.yes() True >>>p.not_yes() # should be False Traceback (most recent call last): File "<pyshell#150>", line 1, in <module> p.not_yes() File "C:\Users\Nona\Desktop\p10.py", line 51, in <lambda> extended_dict["not_" + k] = lambda s, *args, **kw: not v(s, *args, **kw) TypeError: __init__() takes exactly 2 positional arguments (1 given) >>>p.maybe(True) True >>>p.not_maybe(True) #should be False True

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  • Passing mix of T and T[] to a Java varargs method

    - by rfalke
    Suppose you have a Java method void foobar(int id, String ... args) and want to pass both String arrays and Strings into the method. Like this String arr1[]={"adas", "adasda"}; String arr2[]={"adas", "adasda"}; foobar(0, "adsa", "asdas"); foobar(1, arr1); foobar(2, arr1, arr2); foobar(3, arr1, "asdas", arr2); In Python there is "*" for this. Is there some way better than such rather ugly helper method: static String[] concat(Object... args) { List<String> result = new ArrayList<String>(); for (Object arg : args) { if (arg instanceof String) { String s = (String) arg; result.add(s); } else if (arg.getClass().isArray() && arg.getClass().getComponentType().equals(String.class)) { String arr[] = (String[]) arg; for (String s : arr) { result.add(s); } } else { throw new RuntimeException(); } } return result.toArray(new String[result.size()]); } which allows foobar(4, concat(arr1, "asdas", arr2));

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  • How to use Java varargs with the GWT Javascript Native Interface? (aka, "GWT has no printf()")

    - by markerikson
    I'm trying to quickly learn GWT as part of a new project. I found out that GWT doesn't implement Java's String.format() function, so there's no printf()-like functionality. I knew that some printf() implementations exist for Javascript, so I figured I could paste one of those in as a GWT Javascript Native Interface function. I ran into problems, and decided I'd better make sure that the varargs values were being passed in correctly. That's where things got ugly. First, some example code: // From Java, call the JSNI function: test("sourceString", "params1", "params2", "params3"); .... public static native void test(Object... params) /*-{ // PROBLEM: this kills GWT! // alert(params.length); // returns "function" alert(typeof(params)); // returns "[Ljava.lang.Object;@b97ff1" alert(params); }-*/; The GWT docs state that "calling a varargs JavaScript method from Java will result in the callee receiving the arguments in an array". I figured that meant I could at least check params.length, but accessing that throws a JavascriptException wrapped in an UmbrellaException, with no real information. When I do "typeof(params)", it returns "function". As if that weren't odd enough, if I check the string value of params, it returns what appears to be a string version of a Java reference. So, I guess I'm asking a few different questions here: 1) How do GWT/JSNI varargs actually work, and do I need to do something special to pass in values? 2) What is actually going on here? 3) Is there any easier way to get printf()-style formatting in a GWT application?

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  • How to tell a method has a varargs argument using reflection?

    - by Anthony Kong
    Here is a sample code package org.example; import java.lang.reflect.Method; class TestRef { public void testA(String ... a) { for (String i : a) { System.out.println(i); } } public static void main(String[] args){ Class testRefClass = TestRef.class; for (Method m: testRefClass.getMethods()) { if (m.getName() == "testA") { System.out.println(m); } } } } The output is public void org.example.TestRef.testA(java.lang.String[]) So the signature of the method is reported to take a array of String. Is there any mean in the reflection library I can tell that the method is originally declared to take a varargs?

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  • Is there any way to retrieve a float from a varargs function's parameters?

    - by Jared P
    If the function was defined with a prototype which explicitly stated the types of the parameters, eg. void somefunc(int arg1, float arg2); but is implemented as void somefunc(int arg1, ...) { ... } is it possible to use va_arg to retrieve a float? It's normally prevented from doing this because varargs functions have implicit type promotions, like float to double, so trying to retrieve an unpromoted type is unsupported, even though the function is being called with the unpromoted type do to the more specific function prototype. The reason for this is to retrieve arguments of different types at runtime, as part of an obj-c interpreter, where one function will be reused for all different types of methods. This would be best as architecture independent (so that if nothing else the same code works on simulator and on device), although if there is no way to do this then device specific fixes will be accepted.

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  • Is there a Java 1.5 varargs API for slf4j yet?

    - by Josh
    I want to get rid of this lot... public void info(String msg); public void info(String format, Object arg); public void info(String format, Object arg1, Object arg2); public void info(String format, Object[] argArray); ...and replace it with this one... public void info(String format, Object ... args); ...so that my logging syntax doesn't have to change depending on the number of arguments I want to log. There seems to be lots of discussion and work around it, but where is it? Or should I wrap the wrapper that is slf4j?

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  • capture types of varargs parameters

    - by IttayD
    Hi, I'd like to define a method accepting varargs, so that I get the types with which it was called even in the case of nulls. def foo(args: Any*) = .... val s: String = null foo(1, s) // i'd like to be able to tell in foo that args(0) is Int, args(1) is String

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  • Solution to compiler warning for generic varargs

    - by TJR
    A puzzle from this blog. Similar to SO1445233. Given the following source listing, explain why the compiler is producing a warning at invocation to the list method and give a solution for removing the warning without resorting to @SuppressWarnings annotation. public class JavaLanguagePuzzle3 { public static void main(String[] args) { list("1", 2, new BigDecimal("3.5")); } private static <T> List<T> list(T... items) { return Arrays.asList(items); } } Warning: Type safety: A generic array of Object&Serializable&Comparable<?> is created for a varargs parameter

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  • Scala: how to specify varargs as type?

    - by IttayD
    Instead of def foo(configuration: (String, String)*) I'd like to be able to write: type Configuration = (String, String)* def foo(configuration: Configuration) The main use case is to provide an easy method signature when overriding in subclasses

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  • In Lua, how to pass vararg to another function while also taking a peek at them?

    - by romkyns
    It seems that in Lua, I can either pass vararg on to another function, or take a peek at them through arg, but not both. Here's an example: function a(marker, ...) print(marker) print(#arg, arg[1],arg[2]) end function b(marker, ...) print(marker) destination("--2--", ...) end function c(marker, ...) print(marker) print(#arg, arg[1],arg[2]) destination("--3--", ...) end function destination(marker, ...) print(marker) print(#arg, arg[1],arg[2]) end Observe that a only looks at the varargs, b only passes them on, while c does both. Here are the results: >> a("--1--", "abc", "def") --1-- 2 abc def >> b("--1--", "abc", "def") --1-- --2-- 2 abc def >> c("--1--", "abc", "def") --1-- test.lua:13: attempt to get length of local 'arg' (a nil value) stack traceback: ...test.lua:13: in function 'c' ...test.lua:22: in main chunk [C]: ? What am I doing wrong? Am I not supposed to combine the two? Why not?

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  • Cost of using repeated parameters

    - by Palimondo
    I consider refactoring few method signatures that currently take parameter of type List or Set of concrete classes --List[Foo]-- to use repeated parameters instead: Foo*. This would allow me to use the same method name and overload it based on the parameter type. This was not possible using List or Set, because List[Foo] and List[Bar] have same type after erasure: List[Object]. In my case the refactored methods work fine with scala.Seq[Foo] that results from the repeated parameter. I would have to change all the invocations and add a sequence argument type annotation to all collection parameters: baz.doStuffWith(foos:_*). Given that switching from collection parameter to repeated parameter is semantically equivalent, does this change have some performance impact that I should be aware of? Is the answer same for scala 2.7._ and 2.8?

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  • By-name repeated parameters

    - by Green Hyena
    How to pass by-name repeated parameters in Scala? The following code fails to work: scala> def foo(s: (=> String)*) = { <console>:1: error: no by-name parameter type allowed here def foo(s: (=> String)*) = { ^ Is there any other way I could pass a variable number of by name parameters to the method?

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  • Use format strings that contain %1, %2 etc. instead of %d, %s etc. - Linux, C++

    - by rursw1
    Hello, As a follow-up of this question (Message compiler replacement in Linux gcc), I have the following problem: When using MC.exe on Windows for compiling and generating messages, within the C++ code I call FormatMessage, which retrieves the message and uses the va_list *Arguments parameter to send the varied message arguments. For example: messages.mc file: MessageId=1 Severity=Error SymbolicName=MULTIPLE_MESSAGE_OCCURED Language=English message %1 occured %2 times. . C++ code: void GetMsg(unsigned int errCode, wstring& message,unsigned int paramNumber, ...) { HLOCAL msg; DWORD ret; LANGID lang = GetUserDefaultLangID(); try { va_list argList; va_start( argList, paramNumber ); const TCHAR* dll = L"MyDll.dll"; _hModule = GetModuleHandle(dll); ret =::FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE|FORMAT_MESSAGE_IGNORE_INSERTS, _hModule, errCode, lang, (LPTSTR) &msg, 0, &argList ); if ( 0 != ret ) { unsigned int count = 0 ; message = msg; if (paramNumber>0) { wstring::const_iterator iter; for (iter = message.begin();iter!=message.end();iter++) { wchar_t xx = *iter; if (xx ==L'%') count++; } } if ((count == paramNumber) && (count >0)) { ::LocalFree( msg ); ret =::FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_HMODULE, _hModule, errCode, GetUserDefaultLangID(), (LPTSTR) &msg, 0, &argList ); } else if (count != paramNumber) { wstringstream tmp; wstring messNumber; tmp << (errCode & 0xFFFF); tmp >> messNumber; message = message +L"("+ messNumber + L"). Bad Format String. "; } } ::LocalFree( msg ); } catch (...) { message << L"last error: " << GetLastError(); } va_end( argList ); } Caller code: wstring message; GetMsg(MULTIPLE_MESSAGE_OCCURED, message,2, "Error message", 5); Now, I wrote a simple script to generate a .msg file from the .mc file, and then I use gencat to generate a catalog from it. But is there a way to use the formatted strings as they contain %1, %2, etc. and NOT the general (%d, %s...) format? Please note, that the solution has to be generic enough for each possible message with each posible types\ arguments order... Is it possible at all? Thank you.

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