(octave.info)Promotion and Demotion of Data Types

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4.7 Promotion and Demotion of Data Types
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Many operators and functions can work with mixed data types.  For
example,

     uint8 (1) + 1
         ⇒ 2

where the above operator works with an 8-bit integer and a double
precision value and returns an 8-bit integer value.  Note that the type
is demoted to an 8-bit integer, rather than promoted to a double
precision value as might be expected.  The reason is that if Octave
promoted values in expressions like the above with all numerical
constants would need to be explicitly cast to the appropriate data type
like

     uint8 (1) + uint8 (1)
         ⇒ 2

which becomes difficult for the user to apply uniformly and might allow
hard to find bugs to be introduced.  The same applies to single
precision values where a mixed operation such as

     single (1) + 1
         ⇒ 2

returns a single precision value.  The mixed operations that are valid
and their returned data types are

               Mixed Operation        Result
----------------------------------------------------------------------------
               double OP single       single
               double OP integer      integer
               double OP char         double
               double OP logical      double
               single OP integer      integer
               single OP char         single
               single OP logical      single

   The same logic applies to functions with mixed arguments such as

     min (single (1), 0)
        ⇒ 0

where the returned value is single precision.

   In the case of mixed type indexed assignments, the type is not
changed.  For example,

     x = ones (2, 2);
     x(1, 1) = single (2)
        ⇒ x = 2   1
               1   1

where ‘x’ remains of the double precision type.