Understanding Method Structure

Question

Ok forgive me if this seems self explanatory but I've been using C style languages for most of my life and I'm having a hard time with the transition to the Obj-C logic here.
In PHP/Javascript/etc we do this:
php
function functionName( $var1, $var2  ) {
  // Add the 2 vars
}
$varName = functionName( 3, 4 ); // Results in 7

In C we do this (forgive me if this is off, my C is about 13 years rusty):
c
int functionName( int var1, int var2  ) {
  // Add the 2 vars
}
int var1 = 3;
int var2 = 4;
int varName = functionName( var1, var2 ); // Results in 7

According to the video we are doing this for Obj-C:
objc
-(int)functionNameVar1:(int)var1 var2Something:(int)var2 { // Yes functionName is a method now
  // Add the 2 vars
}
int var1 = 3;
int var2 = 4;
int varName = [class functionNameVar1:var1 var2Something:var2 ]; // Results in 7

Ok my question here is understanding, what seems to be, the butchered code in Obj-C. 
Why in Obj-C are combining a var into the name of the method?
Why is there what almost seems to be an unnecessary repetition for the var2Something:(int)var2? ( In the example this would actually look like var2(int)var2 )
Is the var2Something prefix necessary because now we no longer use the parenthesis so the compiler has to know that its a variable of the method being called?
I hope someone can help me wrap my head around this, it just seems overly complicated for such a simple portion of coding.

Ron Casey · Accepted Answer

I'm new to Objective-C, but here's my take thus far.
1) Objective-C method declaration is all about self-documentation. The idea is a person can get a solid grasp on what your method does by simply reading the method name. 
This makes sense if you take a look at some methods provided in the SDKs:
objectivec
- (void)setTitleColor:(UIColor *)color 
             forState:(UIControlState)state;

When calling this method (which is an instance method on UIButton), I can infer I am setting the color of the button for a specific state. I can see which objects I need to pass to UIButton to accomplish that. So when I call the method:
objectivec
[button setTitleColor:redColor forState:Highlighted];

Someone reading my code could easily see I just set the color of my button to red, when the button is in the Highlighted state.
Let's take a look at what this would look like in C:
```c
void setTitleColorForState (UIColor* color, UIControlState state);
button.setTitleColorForState(redColor, Highlighted);
```
Imagine a method that took in lots of objects, like NSBitmapImageRep init:
objectivec
- (id)initWithBitmapDataPlanes:(unsigned char **)planes 
                    pixelsWide:(NSInteger)width 
                    pixelsHigh:(NSInteger)height 
                 bitsPerSample:(NSInteger)bps 
               samplesPerPixel:(NSInteger)spp 
                      hasAlpha:(BOOL)alpha 
                      isPlanar:(BOOL)isPlanar 
                colorSpaceName:(NSString *)colorSpaceName 
                  bitmapFormat:(NSBitmapFormat)bitmapFormat 
                   bytesPerRow:(NSInteger)rowBytes 
                  bitsPerPixel:(NSInteger)pixelBits;

Imagine that in C:
c
image.initWithBitmapDataPlanes (w, h, sample, spp, TRUE, FALSE, colorSpace, bitmapFormat, x, y);

2) Xcode has amazing auto code completion. The vast majority of the time you'll only need to type out your method declaration once, and every time you call it you'll just be entering in object names while hitting tab.
3) Yes. See 1 & 2 for why.

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Understanding Method Structure

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Ron Casey

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