Shortcuts in Objective-C to concatenate NSStrings

An option:

[NSString stringWithFormat:@"%@/%@/%@", one, two, three];

Another option:

I'm guessing you're not happy with multiple appends (a+b+c+d), in which case you could do:

NSLog(@"%@", [Util append:one, @" ", two, nil]); // "one two"
NSLog(@"%@", [Util append:three, @"/", two, @"/", one, nil]); // three/two/one

using something like

+ (NSString *) append:(id) first, ...
{
    NSString * result = @"";
    id eachArg;
    va_list alist;
    if(first)
    {
        result = [result stringByAppendingString:first];
        va_start(alist, first);
        while (eachArg = va_arg(alist, id)) 
        result = [result stringByAppendingString:eachArg];
        va_end(alist);
    }
    return result;
}

Two answers I can think of... neither is particularly as pleasant as just having a concatenation operator.

First, use an NSMutableString, which has an appendString method, removing some of the need for extra temp strings.

Second, use an NSArray to concatenate via the componentsJoinedByString method.

Well, as colon is kind of special symbol, but is part of method signature, it is possible to exted the NSString with category to add this non-idiomatic style of string concatenation:

[@"This " : @"feels " : @"almost like " : @"concatenation with operators"];

You can define as many colon separated arguments as you find useful... ;-)

For a good measure, I've also added concat: with variable arguments that takes nil terminated list of strings.

//  NSString+Concatenation.h

#import <Foundation/Foundation.h>

@interface NSString (Concatenation)

- (NSString *):(NSString *)a;
- (NSString *):(NSString *)a :(NSString *)b;
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c;
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c :(NSString *)d;

- (NSString *)concat:(NSString *)strings, ...;

@end

//  NSString+Concatenation.m

#import "NSString+Concatenation.h"

@implementation NSString (Concatenation)

- (NSString *):(NSString *)a { return [self stringByAppendingString:a];}
- (NSString *):(NSString *)a :(NSString *)b { return [[self:a]:b];}
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c
    { return [[[self:a]:b]:c]; }
- (NSString *):(NSString *)a :(NSString *)b :(NSString *)c :(NSString *)d
    { return [[[[self:a]:b]:c]:d];}

- (NSString *)concat:(NSString *)strings, ...
{
    va_list args;
    va_start(args, strings);

    NSString *s;    
    NSString *con = [self stringByAppendingString:strings];

    while((s = va_arg(args, NSString *))) 
        con = [con stringByAppendingString:s];

    va_end(args);
    return con;
}
@end

//  NSString+ConcatenationTest.h

#import <SenTestingKit/SenTestingKit.h>
#import "NSString+Concatenation.h"

@interface NSString_ConcatenationTest : SenTestCase

@end

//  NSString+ConcatenationTest.m

#import "NSString+ConcatenationTest.h"

@implementation NSString_ConcatenationTest

- (void)testSimpleConcatenation 
{
    STAssertEqualObjects([@"a":@"b"], @"ab", nil);
    STAssertEqualObjects([@"a":@"b":@"c"], @"abc", nil);
    STAssertEqualObjects([@"a":@"b":@"c":@"d"], @"abcd", nil);
    STAssertEqualObjects([@"a":@"b":@"c":@"d":@"e"], @"abcde", nil);
    STAssertEqualObjects([@"this " : @"is " : @"string " : @"concatenation"],
     @"this is string concatenation", nil);
}

- (void)testVarArgConcatenation 
{
    NSString *concatenation = [@"a" concat:@"b", nil];
    STAssertEqualObjects(concatenation, @"ab", nil);

    concatenation = [concatenation concat:@"c", @"d", concatenation, nil];
    STAssertEqualObjects(concatenation, @"abcdab", nil);
}

Shortcut by creating AppendString (AS) macro ...

#define AS(A,B)    [(A) stringByAppendingString:(B)]

NSString *myString = @"This";

NSString *test = AS(myString,@" is just a test");

Note:

If using a macro, of course just do it with variadic arguments, see EthanB's answer.

When building requests for web services, I find doing something like the following is very easy and makes concatenation readable in Xcode:

NSString* postBody = {
    @"<?xml version=\"1.0\" encoding=\"utf-8\"?>"
    @"<soap:Envelope xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\" xmlns:soap=\"http://schemas.xmlsoap.org/soap/envelope/\">"
    @" <soap:Body>"
    @"  <WebServiceMethod xmlns=\"\">"
    @"   <parameter>test</parameter>"
    @"  </WebServiceMethod>"
    @" </soap:Body>"
    @"</soap:Envelope>"
};

The only way to make c = [a stringByAppendingString: b] any shorter is to use autocomplete at around the st point. The + operator is part of C, which doesn't know about Objective-C objects.

NSString *label1 = @"Process Name: ";
NSString *label2 = @"Process Id: ";
NSString *processName = [[NSProcessInfo processInfo] processName];
NSString *processID = [NSString stringWithFormat:@"%d", [[NSProcessInfo processInfo] processIdentifier]];
NSString *testConcat = [NSString stringWithFormat:@"%@ %@ %@ %@", label1, processName, label2, processID];

Inspired by NSMutableString idea from Chris, I make a perfect macro imho. It supports insert nil elements without any Exceptions.

#import <libextobjc/metamacros.h>

#define STR_CONCAT(...) \
    ({ \
        __auto_type str__ = [NSMutableString string]; \
        metamacro_foreach_cxt(never_use_immediately_str_concatify_,, str__, __VA_ARGS__) \
        (NSString *)str__.copy; \
    })

#define never_use_immediately_str_concatify_(INDEX, CONTEXT, VAR) \
    [CONTEXT appendString:VAR ?: @""];

Example:

STR_CONCAT(@"button_bg_", @(count).stringValue, @".png"); 
// button_bg_2.png

If you like, you can use id type as parameter by using [VAR description] instead of NSString.