Top hidden-features Questions

List of Tags
1480
Serhat Özgel

This came to my mind after I learned the following from this question:

where T : struct

We, C# developers, all know the basics of C#. I mean declarations, conditionals, loops, operators, etc.

Some of us even mastered the stuff like Generics, anonymous types, lambdas, LINQ, ...

But what are the most hidden features or tricks of C# that even C# fans, addicts, experts barely know?

Here are the revealed features so far:


Keywords

Attributes

Syntax

Language Features

Visual Studio Features

Framework

Methods and Properties

Tips & Tricks

  • Nice method for event handlers by Andreas H.R. Nilsson
  • Uppercase comparisons by John
  • Access anonymous types without reflection by dp
  • A quick way to lazily instantiate collection properties by Will
  • JavaScript-like anonymous inline-functions by roosteronacid

Other

Answered By: ageektrapped ( 755)

This isn't C# per se, but I haven't seen anyone who really uses System.IO.Path.Combine() to the extent that they should. In fact, the whole Path class is really useful, but no one uses it!

I'm willing to bet that every production app has the following code, even though it shouldn't:

string path = dir + "\\" + fileName;
1423
jelovirt
Answered By: Thomas Wouters ( 743)

Chaining comparison operators:

>>> x = 5
>>> 1 < x < 10
True
>>> 10 < x < 20 
False
>>> x < 10 < x*10 < 100
True
>>> 10 > x <= 9
True
>>> 5 == x > 4
True

In case you're thinking it's doing 1 < x, which comes out as True, and then comparing True < 10, which is also True, then no, that's really not what happens (see the last example.) It's really translating into 1 < x and x < 10, and x < 10 and 10 < x * 10 and x*10 < 100, but with less typing and each term is only evaluated once.

312
Allain Lalonde

What "Hidden Features" of JavaScript do you think every programmer should know?

After having seen the excellent quality of the answers to the following questions I thought it was time to ask it for JavaScript.

Even though JavaScript is arguably the most important Client Side language right now (just ask Google) it's surprising how little most web developers appreciate how powerful it really is.

Answered By: Mark Cidade ( 374)

You don't need to define any parameters for a function. You can just use the function's arguments array-like object.

function sum() {
    var retval = 0;
    for (var i = 0, len = arguments.length; i < len; ++i) {
        retval += arguments[i];
    }
    return retval;
}

sum(1, 2, 3) // returns 6

Inspired by the question series 'Hidden features of ...', I am curious to hear about your favorite Django tips or lesser known but useful features you know of.

  • Please, include only one tip per answer.
  • Add Django version requirements if there are any.
Answered By: Haes ( 222)

I'm just going to start with a tip from myself :)

Use os.path.dirname() in settings.py to avoid hardcoded dirnames.

Don't hardcode path's in your settings.py if you want to run your project in different locations. Use the following code in settings.py if your templates and static files are located within the Django project directory:

# settings.py
import os
PROJECT_DIR = os.path.dirname(__file__)
...
STATIC_DOC_ROOT = os.path.join(PROJECT_DIR, "static")
...
TEMPLATE_DIRS = (
    os.path.join(PROJECT_DIR, "templates"),
)

Credits: I got this tip from the screencast 'Django From the Ground Up'.

232
Chris Noe

What are some of the lesser know, but important and useful features of Windows batch files?

Guidelines:

  • One feature per answer
  • Give both a short description of the feature and an example, not just a link to documentation
  • Limit answers to native funtionality, i.e., does not require additional software, like the Windows Resource Kit

Clarification: We refer here to scripts that are processed by cmd.exe, which is the default on WinNT variants.

(See also: Windows batch files: .bat vs .cmd?)

Answered By: Chris Noe ( 186)

Line continuation:

call C:\WINDOWS\system32\ntbackup.exe ^
    backup ^
    /V:yes ^
    /R:no ^
    /RS:no ^
    /HC:off ^
    /M normal ^
    /L:s ^
    @daily.bks ^
    /F daily.bkf

Visual Studio is such a massively big product that even after years of working with it I sometimes stumble upon a new/better way to do things or things I didn't even know were possible.

For instance-

  • Crtl + R, Ctrl + W to show white spaces. Essential for editing Python build scripts.

  • Under "HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0\Text Editor" Create a String called Guides with the value "RGB(255,0,0), 80" to have a red line at column 80 in the text editor.

What other hidden features have you stumbled upon?

Answered By: shoosh ( 123)

Make a selection with ALT pressed - selects a square of text instead of whole lines.

175
George Mauer

I know this sounds like a point-whoring question but let me explain where I'm coming from.

Out of college I got a job at a PHP shop. I worked there for a year and a half and thought that I had learned all there was to learn about programming.

Then I got a job as a one-man internal development shop at a sizable corporation where all the work was in C#. In my commitment to the position I started reading a ton of blogs and books and quickly realized how wrong I was to think I knew everything. I learned about unit testing, dependency injection and decorator patterns, the design principle of loose coupling, the composition over inheritance debate, and so on and on and on - I am still very much absorbing it all. Needless to say my programming style has changed entirely in the last year.

Now I find myself picking up a php project doing some coding for a friend's start-up and I feel completely constrained as opposed to programming in C#. It really bothers me that all variables at a class scope have to be referred to by appending '$this->' . It annoys me that none of the IDEs that I've tried have very good intellisense and that my SimpleTest unit tests methods have to start with the word 'test'. It drives me crazy that dynamic typing keeps me from specifying implicitly which parameter type a method expects, and that you have to write a switch statement to do method overloads. I can't stand that you can't have nested namespaces and have to use the :: operator to call the base class's constructor.

Now I have no intention of starting a PHP vs C# debate, rather what I mean to say is that I'm sure there are some PHP features that I either don't know about or know about yet fail to use properly. I am set in my C# universe and having trouble seeing outside the glass bowl.

So I'm asking, what are your favorite features of PHP? What are things you can do in it that you can't or are more difficult in the .Net languages?

Answered By: Kyle Cronin ( 330)

Documentation. The documentation gets my vote. I haven't encountered a more thorough online documentation for a programming language - everything else I have to piece together from various websites and man pages.

160
squadette

Continuing the "Hidden features of ..." meme, let's share the lesser-known but useful features of Ruby programming language.

Try to limit this discussion with core Ruby, without any Ruby on Rails stuff.

See also:

(Please, just one hidden feature per answer.)

Thank you

Answered By: Farrel ( 80)

From Ruby 1.9 Proc#=== is an alias to Proc#call, which means Proc objects can be used in case statements like so:

def multiple_of(factor)
  Proc.new{|product| product.modulo(factor).zero?}
end

case number
  when multiple_of(3)
    puts "Multiple of 3"
  when multiple_of(7)
    puts "Multiple of 7"
end
149
Krzysiek Goj

What are the hidden features of Scala that every Scala developer should be aware of?

One hidden feature per answer, please.

Answered By: Willis Blackburn ( 85)

Okay, I had to add one more. Every Regex object in Scala has an extractor (see answer from oxbox_lakes above) that gives you access to the match groups. So you can do something like:

// Regex to split a date in the format Y/M/D.
val regex = "(\\d+)/(\\d+)/(\\d+)".r
val regex(year, month, day) = "2010/1/13"

The second line looks confusing if you're not used to using pattern matching and extractors. Whenever you define a val or var, what comes after the keyword is not simply an identifier but rather a pattern. That's why this works:

val (a, b, c) = (1, 3.14159, "Hello, world")

The right hand expression creates a Tuple3[Int, Double, String] which can match the pattern (a, b, c).

Most of the time your patterns use extractors that are members of singleton objects. For example, if you write a pattern like

Some(value)

then you're implicitly calling the extractor Some.unapply.

But you can also use class instances in patterns, and that is what's happening here. The val regex is an instance of Regex, and when you use it in a pattern, you're implicitly calling regex.unapplySeq (unapply versus unapplySeq is beyond the scope of this answer), which extracts the match groups into a Seq[String], the elements of which are assigned in order to the variables year, month, and day.

144
Adam Bellaire

What are some really useful but esoteric language features in Perl that you've actually been able to employ to do useful work?

Guidelines:

  • Try to limit answers to the Perl core and not CPAN
  • Please give an example and a short description

Hidden Features also found in other languages' Hidden Features:

(These are all from Corion's answer)

  • C
    • Duff's Device
    • Portability and Standardness
  • C#
    • Quotes for whitespace delimited lists and strings
    • Aliasable namespaces
  • Java
    • Static Initalizers
  • JavaScript
    • Functions are First Class citizens
    • Block scope and closure
    • Calling methods and accessors indirectly through a variable
  • Ruby
    • Defining methods through code
  • PHP
    • Pervasive online documentation
    • Magic methods
    • Symbolic references
  • Python
    • One line value swapping
    • Ability to replace even core functions with your own functionality

Other Hidden Features:

Operators:

Quoting constructs:

Syntax and Names:

Modules, Pragmas, and command-line options:

Variables:

Loops and flow control:

Regular expressions:

Other features:

Other tricks, and meta-answers:


See Also:

Answered By: John Siracusa ( 54)

The flip-flop operator is useful for skipping the first iteration when looping through the records (usually lines) returned by a file handle, without using a flag variable:

while(<$fh>)
{
  next if 1..1; # skip first record
  ...
}

Run perldoc perlop and search for "flip-flop" for more information and examples.