How to make inline functions in C

Question

I m using Linq To XML  new XElement  Prefix   Prefix    null        Prefix    but I want to do some computation to the prefix before adding it to the xml  like eliminating spaces  special chars  some calculations etc   I don t want to create functions because this ones won t be of any help on any other part of my program but this  so is there any way to create inline functions

User · Answer

Yes   You can create anonymous methods or lambda expressions   Func lt string  string gt  PrefixTrimmer   delegate string x        return x           Func lt string  string gt  PrefixTrimmer   x   gt  x

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C  7 adds support for local functions  Here is the previous example using a local function  void Method         string localFunction string source                   add your functionality here         return source                 call the inline function    localFunction  prefix

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The answer to your question is yes and no  depending on what you mean by  inline function    If you re using the term like it s used in C   development then the answer is no  you can t do that - even a lambda expression is a function call   While it s true that you can define inline lambda expressions to replace function declarations in C   the compiler still ends up creating an anonymous function   Here s some really simple code I used to test this  VS2015        static void Main string   args                Func lt int  int gt  incr   a   gt  a   1          Console WriteLine   P1    incr 5              What does the compiler generate   I used a nifty tool called ILSpy that shows the actual IL assembly generated   Have a look  I ve omitted a lot of class setup stuff   This is the Main function           IL 001f  stloc 0         IL 0020  ldstr  P1    0           IL 0025  ldloc 0         IL 0026  ldc i4 5         IL 0027  callvirt instance  1 class  mscorlib System Func 2 lt int32  int32 gt   Invoke  0          IL 002c  box  mscorlib System Int32         IL 0031  call string  mscorlib System String  Format string  object          IL 0036  call void  mscorlib System Console  WriteLine string          IL 003b  ret   See those lines IL 0026 and IL 0027   Those two instructions load the number 5 and call a function   Then IL 0031 and IL 0036 format and print the result   And here s the function called            method assembly hidebysig              instance int32   lt Main gt b  0 0                    int32 a               cil managed                           Method begins at RVA 0x20ac                Code size 4  0x4               maxstack 8              IL 0000  ldarg 1             IL 0001  ldc i4 1             IL 0002  add             IL 0003  ret              end of method   lt  gt c     lt Main gt b  0 0    It s a really short function  but it is a function   Is this worth any effort to optimize   Nah   Maybe if you re calling it thousands of times a second  but if performance is that important then you should consider calling native code written in C C   to do the work     In my experience readability and maintainability are almost always more important than optimizing for a few microseconds gain in speed   Use functions to make your code readable and to control variable scoping and don t worry about performance    Premature optimization is the root of all evil   or at least most of it  in programming   -- Donald Knuth   A program that doesn t run correctly doesn t need to run fast  -- Me

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You can use Func which encapsulates a method that has one parameter and returns a value of the type specified by the TResult parameter   void Method         Func lt string string gt  inlineFunction   source   gt                    add your functionality here         return source                    call the inline function    inlineFunction  prefix

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Yes  C  supports that  There are several syntaxes available    Anonymous methods were added in C  2 0   Func lt int  int  int gt  add   delegate int x  int y        return x   y     Action lt int gt  print   delegate int x        Console WriteLine x     Action lt int gt  helloWorld   delegate    parameters can be elided if ignored       Console WriteLine  Hello world        Lambdas are new in C  3 0 and come in two flavours    Expression lambdas   Func lt int  int  int gt  add    int x  int y    gt  x   y     or    Func lt int  int  int gt  add    x  y    gt  x   y     types are inferred by the compiler  Statement lambdas   Action lt int gt  print    int x    gt    Console WriteLine x      Action lt int gt  print   x   gt    Console WriteLine x         inferred types Func lt int  int  int gt  add    x  y    gt    return x   y       Local functions have been introduced with C  7 0   int add int x  int y    gt  x   y  void print int x    Console WriteLine x        There are basically two different types for these  Func and Action  Funcs return values but Actions don t  The last type parameter of a Func is the return type  all the others are the parameter types   There are similar types with different names  but the syntax for declaring them inline is the same  An example of this is Comparison lt T gt   which is roughly equivalent to Func lt T  T  int gt    Func lt string  string  int gt  compare1    l r    gt  1  Comparison lt string gt  compare2    l  r    gt  1  Comparison lt string gt  compare3   compare1     this one only works from C  4 0 onwards   These can be invoked directly as if they were regular methods   int x   add 23  17      x    40 print x      outputs 40 helloWorld x      helloWorld has one int parameter declared  Action lt int gt                    even though it does not make any use of it

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Not only Inside methods  it can be used inside classes also   class Calculator               public static int Sum int x int y    gt  x   y          public static Func lt int  int  int gt   Add    x  y    gt  x   y          public static Action lt int int gt  DisplaySum    x  y    gt  Console WriteLine x   y

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