Water 5-Syntax and Fundamentals-Variable: Local and Field

Contract
Return type	wob
Parameter key	Default value	Type
place	req
new_value	req

Water Contract
<method set_value place =req new_value=req/>

See also: set, active_value

Note that normally 'set' is used instead of set_value. Use set_value only when you want the key that is to be set to be computed. Please read the documentation on 'set' before reading about set_value. The first argument is the place to set, the second is the new value. Both arguments are executed. <set_value place new_value/> Local variables:

<set_value "foo" 1.<plus 2/> />
foo

foo will be bound until the end of the method body that its in. If we've called execute_string on a string that has several top level expressions, then foobar will be bound throughout, i.e. one local environment for the entire string. Field Variables:

thing.<set_value "foo" <thing/>/>
thing.foo

<thing/>

thing.foo.<set_value "baz" 2/>
thing.foo.baz

Below here are advanced uses of set_value not needed for simple programming. These take advantage of the fact that set_value sets a key that is the result of executing its first argument. Computing Place

thing.<set_value "my".<join "place"/> "red"/>
thing.myplace

"red"

Fluid Variables: Fluid variables can be set by calling set_value with a _subject of fluid. Unlike local variables, they have DYNAMIC extent. Fluid variables shadow previously set stack variables. In the example below, we set up two (nested) fluid variables each named test7. For the execution of the BODY of the inner set, the inner $test7 i.e. the one with value 77, shadows the one with value 777. When the inner set is called, first test7 and 77 are pushed onto the fluid variable "stack", then the content of the set is executed. First we call the method test_meth2 which causes test_meth to be called, which executes the fluid variable test7, whose value is looked up on the stack to get 77 which is returned by both methods and ultimately by the inner set then finally the outer set. Example:

<method test_meth2> <test_meth/> </>
<method test_meth> fluid.test7</>
fluid.<set test7=777>
   fluid.<set test7=77>
      <test_meth2/>
   </set>
 </set>

You can test that a fluid variable existis by using has just as in any other object:

fluid.<set test8=88>
   fluid.<has "test8"/>
</set>

true

You can compute the name of a fluid to set. Here's a rather tricky example:

<set myvar="foo97">
         fluid.<set_value myvar 4>
                   fluid.<get myvar/>
               </set_value>
    </set>

First the local variable myvar is bound to "foo97". Next in our call to set_value we use the value of myvar, i.e. "foo97" as the name of the fluid variable to set to 4. Finally within the content of call to fluid.set we execute the expression fluid.<get myvar/> which is effectively fluid.foo97 , whose value is 4 .