In my code i have a lot of code like:
if (block) block(....)
So I want to define a macro, something like
#define safetyCall(block, ...) if((block)) {block(##__VA_ARGS__)};
But i couldn't get it to work. Any idea?
You don't need the ## and the ; needs moving:
#define safetyCall(block, ...) if((block)) { block(__VA_ARGS__); }
This can run into issues if your block is inline and contains code that has a series of comma separated strings, etc.
Example:
safetyCall(^void() {
NSArray *foo = #[#"alice", "bob"];
};
The compiler will complain about "Expected ']' or '.'" and "Expected identifier or '('".
However, if you were to declare the inline block as a separate block before the macro, it will not generate an error.
Example:
void (^fooBlock)(void) = ^void() {
NSArray *foo = #[#"alice", #"bob"];
}
safetyCall(fooBlock);
Related
In my code i have a lot of code like:
if (block) block(....)
So I want to define a macro, something like
#define safetyCall(block, ...) if((block)) {block(##__VA_ARGS__)};
But i couldn't get it to work. Any idea?
You don't need the ## and the ; needs moving:
#define safetyCall(block, ...) if((block)) { block(__VA_ARGS__); }
This can run into issues if your block is inline and contains code that has a series of comma separated strings, etc.
Example:
safetyCall(^void() {
NSArray *foo = #[#"alice", "bob"];
};
The compiler will complain about "Expected ']' or '.'" and "Expected identifier or '('".
However, if you were to declare the inline block as a separate block before the macro, it will not generate an error.
Example:
void (^fooBlock)(void) = ^void() {
NSArray *foo = #[#"alice", #"bob"];
}
safetyCall(fooBlock);
I am using libclang to parse a objective c source code file. The following code finds all Objective-C instance method declarations, but it also finds declarations in the includes:
enum CXCursorKind curKind = clang_getCursorKind(cursor);
CXString curKindName = clang_getCursorKindSpelling(curKind);
const char *funcDecl="ObjCInstanceMethodDecl";
if(strcmp(clang_getCString(curKindName),funcDecl)==0{
}
How can I skip everything, which comes from header includes? I am only interested in my own Objective-C instance method declarations in the source file, not in any of the includes.
e.g. the following should not be included
...
Location: /System/Library/Frameworks/Foundation.framework/Headers/NSObject.h:15:9:315
Type:
TypeKind: Invalid
CursorKind: ObjCInstanceMethodDecl
...
Answering this question because I couldn't believe that hard-coding paths comparisons was the only solution, and indeed, there is a clang_Location_isFromMainFile function that does exactly what you want, so that you can filter unwanted results in the visitor, like this :
if (clang_Location_isFromMainFile (clang_getCursorLocation (cursor)) == 0) {
return CXChildVisit_Continue;
}
The only way I know would be to skip unwanted paths during the AST visit. You can for example put something like the following in your visitor function. Returning CXChildVisit_Continue avoids visiting the entire file.
CXFile file;
unsigned int line, column, offset;
CXString fileName;
char * canonicalPath = NULL;
clang_getExpansionLocation (clang_getCursorLocation (cursor),
&file, &line, &column, &offset);
fileName = clang_getFileName (file);
if (clang_getCString (fileName)) {
canonicalPath = realpath (clang_getCString (fileName), NULL);
}
clang_disposeString (fileName);
if (strcmp(canonicalPath, "/canonical/path/to/your/source/file") != 0) {
return CXChildVisit_Continue;
}
Also, why compare CursorKindSpelling instead of the CursorKind directly?
I'm having a strange crash, at the 4th line below.
{
...
int exp = [[resourceCompletionReward objectAtIndex:experienceD] integerValue];
int xx = mySprite.x;
int yy = mySprite.y;
[self setupRisingText:exp withX:xx withY:yy];
...
}
-(void)setupRisingText:(int)risingValue withX:xx withY:yy {
...
}
When it tries to run the setupRising Text method it just crashes. Can't see anything wrong though?
What ever you do with xx and yy in setupRisingText::: they are treated as id (something like NSObject *, not exactly like that but similar)
So instead of int variables pointers to objects (any object, not just subclasses of NSObject) are accessed and dealt with. That is the default for any parameter without a type.
Use
-(void)setupRisingText:(int)risingValue withX:(int)xx withY:(int)yy {
...
}
instead.
BTW, if you used NSNumber you would have less of a problem here.
I am wondering, shouldn't your method look like this?
-(void)setupRisingText:(int)risingValue withX:(int)xx withY:(int)yy {
//NSLog(#"%d",risingValue+xx+yy);
}
When declaring a block what's the rationale behind using this syntax (i.e. surrounding brackets and caret on the left)?
(^myBlock)
For example:
int (^myBlock)(int) = ^(int num) {
return num * multiplier;
};
C BLOCKS: Syntax and Usage
Variables pointing to blocks take on the exact same syntax as variables pointing to functions, except * is substituted for ^. For example, this is a function pointer to a function taking an int and returning a float:
float (*myfuncptr)(int);
and this is a block pointer to a block taking an int and returning a float:
float (^myblockptr)(int);
As with function pointers, you'll likely want to typedef those types, as it can get relatively hairy otherwise. For example, a pointer to a block returning a block taking a block would be something like void (^(^myblockptr)(void (^)()))();, which is nigh impossible to read. A simple typedef later, and it's much simpler:
typedef void (^Block)();
Block (^myblockptr)(Block);
Declaring blocks themselves is where we get into the unknown, as it doesn't really look like C, although they resemble function declarations. Let's start with the basics:
myvar1 = ^ returntype (type arg1, type arg2, and so on) {
block contents;
like in a function;
return returnvalue;
};
This defines a block literal (from after = to and including }), explicitly mentions its return type, an argument list, the block body, a return statement, and assigns this literal to the variable myvar1.
A literal is a value that can be built at compile-time. An integer literal (The 3 in int a = 3;) and a string literal (The "foobar" in const char *b = "foobar";) are other examples of literals. The fact that a block declaration is a literal is important later when we get into memory management.
Finding a return statement in a block like this is vexing to some. Does it return from the enclosing function, you may ask? No, it returns a value that can be used by the caller of the block. See 'Calling blocks'. Note: If the block has multiple return statements, they must return the same type.
Finally, some parts of a block declaration are optional. These are:
The argument list. If the block takes no arguments, the argument list can be skipped entirely.
Examples:
myblock1 = ^ int (void) { return 3; }; // may be written as:
myblock2 = ^ int { return 3; }
The return type. If the block has no return statement, void is assumed. If the block has a return statement, the return type is inferred from it. This means you can almost always just skip the return type from the declaration, except in cases where it might be ambiguous.
Examples:
myblock3 = ^ void { printf("Hello.\n"); }; // may be written as:
myblock4 = ^ { printf("Hello.\n"); };
// Both succeed ONLY if myblock5 and myblock6 are of type int(^)(void)
myblock5 = ^ int { return 3; }; // can be written as:
myblock6 = ^ { return 3; };
source: http://thirdcog.eu/pwcblocks/
I think the rationale is that it looks like a function pointer:
void (*foo)(int);
Which should be familiar to any C programmer.
I was wondering if there were a way to get back how far into an assembly a PKParser has parsed before encountering a syntax error.
reference: http://parsekit.com/
I'm using a grammar that basically describes a prefix notation expression language.
For example:
given your standard prefix notation expression grammar and a string "(+ a - b c))"
I'd like to retrieve that [(,+,a] where matched, so I can give the user some idea of where to look to fix their error, but the completeMatchFor and bestMatchFor don't return anything I can use to find this info.
Ideally I'd like to say that a '(' was expected, but it's not necessary for a grammar as simple as what I'm using.
From the book mentioned as the user manual, it seemed as if I would need to create a custom parser for this, but I was hoping that maybe I'd simply missed something in the framework.
Thoughts?
Developer of ParseKit here.
There are two features in ParseKit which can be used to help provide user-readable hints describing parse errors encountered in input.
-[PKParser bestMatchFor:]
The PKTrack class
It sounds like you're aware of the -bestMatchFor: method even if it's not doing what you expect in this case.
I think the PKTrack class will be more helpful here. As described in Metsker's book, PKTrack is exactly like PKSequence except that its subparsers are required, and an error is thrown (with a helpful error message) when all of its subparsers are not matched.
So here's a grammar for your example input:
#start = '(' expr ')' | expr;
expr = ('+' | '-') term term;
term = '(' expr ')' | Word;
Any productions listed contiguously are a Sequence -- but could instead be a Track.
The benefit of changing these Sequences to be Tracks is that an NSException will be thrown with a human-readable parse error message if the input doesn't match. The downside is that you must now wrap all usages of your factory-generated parser in a try/catch block to catch these Track exceptions.
The problem currently (or before now, at least) is that the PKParserFactory never produced a parser using Tracks. Instead, it would always use Sequences.
So I've just added a new option in head of trunk at Google Code (you'll need to udpate).
#define USE_TRACK 0
in
PKParserFactory.m
It's 0 by default. If you change this define to 1, Tracks will be used instead of Sequences. So given the grammar above and invalid input like this:
(+ a - b c))
and this client code:
NSString *g = // fetch grammar above
PKParser *p = [[PKParserFactory factory] parserFromGrammar:g assembler:self];
NSString *s = #"(+ a - b c))";
#try {
PKAssembly *res = [p parse:s];
NSLog(#"res %#", res);
}
#catch (NSException *exception) {
NSLog(#"Parse Error:%#", exception);
}
you will get a nice-ish human-readable error:
Parse Error:
After : ( + a
Expected : Alternation (term)
Found : -
Hope that helps.
I'm wrestling with this issue too. In order for -bestMatchFor: to be useful in identifying error conditions, there should be methods in PKAssembly's public interface indicating if there are more tokens/characters to be parsed. -completeMatchFor: is able to determine error state because it has access to the private -hasMore method. Perhaps PKAssembly's -hasMore method should be public.
I looked at PKTrack but since I want to handle errors programmatically, it wasn't useful to me.
My conclusion is I either write my own custom Track parser or I alter the framework and expose -hasMore. Are there other ways to handle errors?
Until I figure out a better way to detect errors, I've added the following to the file containing the implementation of my custom parser:
#interface PKAssembly ()
- (BOOL)hasMore;
- (id)peek;
#end
#implementation PMParser
...
#end
In my parse method:
PKAssembly* a = [PKTokenAssembly assemblyWithString:s];
PKAssembly* best = [self bestMatchFor:a];
PMParseNode* node = nil;
BOOL error = NO;
NSUInteger errorOffset = 0;
if (best == nil) // Anything recognized?
{
error = YES;
}
else
{
if ([best hasMore]) // Partial recognition?
{
PKToken* t = [best peek];
error = YES;
errorOffset = t.offset;
}
node = [best pop];
}
If an error occurred, errorOffset will contained the location of the unrecognized token.