The codegolf object

Question

Imagine this, we have an environment with a global scope containing just a single object, called codegolf. This object has a single child called stackexchange, which has a property called com.
Accessing this property would look like codegolf.stackexchange.com.

The challenge

The input of your program/function will be a string trying to access a property on the global scope. Whenever this property is found, you shall print/return a truthy value. If the property isn't found, a falsy value shall be printed/returned. The catch: when you try to access a property on a non-existant object, your program should throw any kind of error¹.

To make things a bit easier, you may assume that input will always be [a-z.], it will never be empty, it will never have repeating .'s and it will never start or end with a .. So codegolf. is an invalid input.

Test cases

codegolf.stackexchange.com => 1 // or any other truthy value
codegolf.stackexchange.net => 0 // or any other falsy value
codegolf.stackexchange => 1
codegolf.foo => 0
codegolf => 1
foo => 0
codegolf.com => 0
codegolf.constructor => 0

codegolf.foo.bar => Error (since foo is undefined)
codegolf.stackexchange.com.foo => Error (since com is a value, not an object)
codegolf.stackexchange.com.foo.bar => Error
foo.stackexchange.com => Error
foo.bar => Error
foo.bar.baz => Error

This is code-golf, shortest code in bytes wins

¹ if (and only if) your language of choice doesn't support errors at all, you must output something which makes it clear that this is an error. For example, if you use 1 for truthy and 0 for falsy, you may use "e" for an error. Be consistent in your return values and explain the behaviour in your post.

Answer 1

JavaScript, 135 bytes

v=>(c=(p,i)=>new Proxy({}, {get:(o,q)=>(r=q==p[i]?c(p,i+1):o.$,i==3?r||z:r)}),x=c(["codegolf","stackexchange","com"],0),!!eval("x."+v))

Reworked the first attempt to prevent builtin keys being accessible, at this point its going to be better to use a different approach, but hey!

Returns true for valid, false for missing and errors on error.

Answer 2

JavaScript (ES6), 87 bytes

Returns false/ true or throws ReferenceError.

s=>s.split`.`.map((w,i)=>e|['codegolf','stackexchange','com'][i]!=w&&e++,e=0)&&e>1?X:!e

let f =
    
s=>s.split`.`.map((w,i)=>e|['codegolf','stackexchange','com'][i]!=w&&e++,e=0)&&e>1?X:!e

console.log(f('codegolf.stackexchange.com')); // => true
console.log(f('codegolf.stackexchange.net')); // => false
console.log(f('codegolf.stackexchange'));     // => true
console.log(f('codegolf.foo'));               // => false
console.log(f('codegolf'));                   // => true
console.log(f('foo'));                        // => false
console.log(f('codegolf.com'));               // => false

console.log(f('codegolf.foo.bar'));           // => Error

Probabilistic version, 78 bytes (non-competing)

Because all properties are guaranteed to match [a-z], we can give this a try:

s=>s.split`.`.map((w,i)=>e|[162,6,2][i]-parseInt(w,36)%587&&e++,e=0)&&e>1?X:!e

Apart from the fact that 587 is a prime and leads to rather short values for the words we are interested in, this is a rather random modulo choice.

Although it does pass all test cases, it is of course likely to return false-positives.

let f =
    
s=>s.split`.`.map((w,i)=>e|[162,6,2][i]-parseInt(w,36)%587&&e++,e=0)&&e>1?X:!e

console.log(f('codegolf.stackexchange.com')); // => true
console.log(f('codegolf.stackexchange.net')); // => false
console.log(f('codegolf.stackexchange'));     // => true
console.log(f('codegolf.foo'));               // => false
console.log(f('codegolf'));                   // => true
console.log(f('foo'));                        // => false
console.log(f('codegolf.com'));               // => false

console.log(f('codegolf.foo.bar'));           // => Error

Answer 3

Batch, 269 231 bytes

@echo off
set/ps=
set w=1codegolf
for %%a in (%s:.= %)do call:l %%w
echo %w:~0,1%
exit/b
:g
if
:l
if %w:~-1%==. goto g
if not %1==%w% set w=0.&exit/b
set w=1com
if %1==com set w=1.
if %1==codegolf set w=1stackexchange

Takes input on STDIN; throws a syntax error for an invalid property. Works by using w as a state machine. If w ends with a . this means that the next property access is invalid. Edit: Saved 17 bytes by using the syntax error to abort the batch script. Saved 21 bytes by realising that one of my assignments could be unconditional.

Answer 4

Javascript, 84 82 bytes

Not short enough to win, but since I am a beginner I thought it would be fun to share it. Maybe someone has a suggestion for improvement.

s=>s.split`.`.length>3&&e||!!eval('codegolf={stackexchange:{com:true}};window.'+s)

It passes all the tests in the question, returns true for existing value, false for non-existent and it throws an error if you try to get a property of a non-existent or non-object variable. However I now realize that this solution has some issues as well. As pointed out by @Florent in the comments it returns true when string prototype properties such as .toString are called.

Edit: 2 bytes shorter thanks to @MamaFunRoll

Test snippet:

var f =
s=>s.split`.`.length>3&&e||!!eval('codegolf={stackexchange:{com:true}};window.'+s)

console.log(f('codegolf.stackexchange.com')) //true
console.log(f('codegolf.stackexchange.net')) //false
console.log(f('codegolf.stackexchange')) //true
console.log(f('codegolf.foo')) //false
console.log(f('codegolf')) //true
console.log(f('foo')) //false
console.log(f('codegolf.com')) //false

console.log(f('codegolf.foo.bar')) // TypeError
console.log(f('codegolf.stackexchange.com.foo')) //ReferenceError
console.log(f('codegolf.stackexchange.com.foo.bar')) //ReferenceError
console.log(f('foo.stackexchange.com')) // TypeError
console.log(f('foo.bar')) // TypeError
console.log(f('foo.bar.baz')) // TypeError

Answer 5

C, 98 112 113 bytes

f(char*a){char*c="codegolf.stackexchage.com";while(*c&&*c==*a)++a,++c;return strchr(a,46)?*(a=0):!(*a|*c&*c-46);}

ungolfed

f(char*a){char*c="codegolf.stackexchage.com";
          while(*c&&*c==*a)++a,++c;
          return strchr(a,46)?*(a=0):!(*a|*c&*c-46);
         }

f(codegolf.stackexchage.com)=1
f(codegolf.stackexchage.net)=0
f(codegolf.stackexchage)=1
f(codegolf.foo)=0
f(codegolf)=1
f(foo)=0

for the below it has to seg fault

f(codegolf.stackexchage.com.foo)
f(foo.bar)
f(foo.bar.baz)
f(codegolf.foo.bar)
f(foo.v)

Answer 6

JavaScript, 173 bytes

function d(a){var b="codegolf",u="stackexchange",c=a.split("."),e="e";return c.length==1?c[0]==b:c.length==2?c[0]==b?c[1]==u:e:c.length==3?c[0]==b?c[1]==u?c[2]=="com":e:e:e}

Works with IE 10, so should work on major modern browsers.

Try it here (+ ungolfed)

Answer 7

C#, 155 bytes

Wasn't going to be the shortest but thought it would be fun give it a go in C#...

bool f(string s){var a=s.Split('.');int e=0,l=a.Length-1,i=l;for(;0<=i;i--){e+=a[i]!=new[]{"codegolf","stackexchange","com"}[i]?i<l?s[-1]:1:0;}return e<1;}

• Splits the string and reverse iterates through the result.
• A non matching element more than 1 iteration deep, errors (throwing an IndexOutOfRangeException by accessing a char at -1 position in the string).
• Otherwise, returns false if any elements didn't match.

.NET Fiddle

Answer 8

Ruby, 84 80 bytes

Anonymous function which returns true or false, or divides by zero to raise error:

->s{k=1;s.split(?.).zip(%w[codegolf stackexchange com]){|i,o|1/0if !k;k=i==o};k} 

Try it online

Answer 9

Java, 187 138 bytes

Version 2.0(138 bytes): Idea shamelessly stolen from @Jamie.

l->{for(String []a=l.split,int l=i=a.length-1,e=0;i>=0;e+=a[i]!=new String[]{"codegolf","stackexchange","com"}[i]?i<l?s[-1]:1:0)return e;}

Version 1.0(187 bytes):

l->{String[]a=l.split(".");return a[0].equals("codegolf")?(a.length<2?1:(a[1].equals("stackexchange")?(a.length<3?1:(a[2].equals("com")?1:0)):(a.length<3?0:a[-1]))):(a.length<2?0:a[-1]);}

Explanation of the return part:

return a[0].equals("codegolf")?(a.length<2?1:(a[1].equals("stackexchange")?(a.length<3?1:(a[2].equals("com")?1:0)):(a.length<3?0:a[-1]))):(a.length<2?0:a[-1]);
return                                                                                                                                                        ;
       a[0].equals("codegolf")?                                                                                                          :
                               (a.length<2? :                                                                                           ) (a.length<2? :     )
                                           1 (a[1].equals("stackexchange")?                                       :                    )              0 a[-1]
                                                                           (a.length<3? :                        ) (a.length<3? :     )
                                                                                       1 (a[2].equals("com")? : )              0 a[-1]
                                                                                                             1 0