Fuzion • Tutorial • Type unit

Type `unit`

The most fundamental types in Fuzion are unit and void

A unit type is a type that has only one possible value. Passing a value of unit type to a function or assigning it to a field does not pass any actual information around.

The unit type hence plays a role similar to type void in Java or C++ code. A difference is that the value of unit type can be produced explicitly by calling its constructor unit. The following example uses this to explicitly return an instance of type unit by feature print3times:

print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  unit;      # explicit unit result
}

res := print3times("Hello!");
say(res);

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print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  unit;      # explicit unit result
}
res := print3times("Hello!");
say(res);
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

If we do not return unit explicitly, the result is that of the last call to say, which happens to be unit:

print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);   # implicitly return unit result from say
}

res := print3times("Hello!");
say(res);

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print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);   # implicitly return unit result from say
}
res := print3times("Hello!");
say(res);
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

In case the last statement in a feature with result type unit does not result in a unit value, we get an error:

print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  msg.byte_length; # error: i32 byte_length is incompatible to unit
}

res := print3times("Hello!");
say(res);

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print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  msg.byte_length; # error: i32 byte_length is incompatible to unit
}
res := print3times("Hello!");
say(res);
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

The result of an empty block is unit, so we can return {} explicitly:

print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  { }        # empty code block results in unit value
}

res := print3times("Hello!");
say(res);

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print3times (msg String) unit => {
  say(msg);
  say(msg);
  say(msg);
  { }        # empty code block results in unit value
}
res := print3times("Hello!");
say(res);
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

or have unit as the implicit result of an empty feature:

do_nothing (ignore String) unit => {
  # empty code block results in unit value
}

res := do_nothing("Hello!");
say(res);

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do_nothing (ignore String) unit => {
  # empty code block results in unit value
}
res := do_nothing("Hello!");
say(res);
 
 
הההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההההה
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What are effects?

last changed: 2024-06-28

next: Type void

Type unit

Type `unit`