B4P Reference

Introduction

The past examples have been made with simple references. However B4P also allows declaring member variables in structures and arrays as references. Here, a similar rule applies that references can only be made on member variables which are not yet existing or do not contain their own sub-members. Two code examples below illustrate this powerful feature.

Example 1

In the following example, 3 members in variable c[] point to variable a[] and a[g] accordingly. In addition, a[g] is a reference which referst to c[]. An "eight-loop" has been created, and the code example demonstrates that you can walk the path through the loop multiple times.
References in Member Variables 2

// Black part in illustration



a[] = Ha;

a[b] = He;

c[] = Hi;



// Greeen part in illustration



c[d] = ^a[];

c[e] = ^a[b];

c[f] = ^c[e]; // references to a[b]

echo( c[d],", ", c[e] ); // Ha,He



// Blue part of illustration



a[g] = ^c[];

echo( a[g],", ", a[g,d] ); // Hi, Ha



// You can loop around multiple times if you wish:



echo( a[g,d,b] ); // He

echo( a[g,d,g],", ", a[g,d,g,d], ", ", a[g,d,g,d,g] ); // Hi, Ha, Hi

Ha, He
Hi, Ha
He
Hi, Ha, Hi

Try it yourself: Open LAN_Features_References_in_member_variables.b4p in B4P_Examples.zip. Decompress before use.

Example 2



// Black part in illustration



array( a[ ],{Ha,He,Hi,Ho} );



// Green part in illustration



a[0] =^  a[3];

a[1] =^^ a[0]; // a[1] refers to a[0] (and not to a[3] directly)



echo( a[0],", ", a[1] ); // Ho, Ho



// Blue part in illustration



a[0] =^ a[2];

echo( a[0],", ", a[1] ); // Hi, Hi

Ho, Ho
Hi, Hi

Try it yourself: Open LAN_Features_References_in_member_variables_01.b4p in B4P_Examples.zip. Decompress before use.

Avoid Tail-Biting

Be aware that you do not build up references resembling infinite loops because B4P will start circling around through 1 or more variables. See the following code examples with one variables and the tail-biting effect with two variables.

       // Bad example 1: 1 dog runs in a circle, attempting to bite its own tail 

       a[] = a[];



       // Bad example 2: 2 dogs run in a circle, attempting to bite each other's tails

       x[] = 5;

       y[] =^x[];

       x[] =^y[];