guideline

Use fixed-size components for records when measured performance indicates.

subtype Line_Range   is Integer range 0 .. Max_Lines;
subtype Length_Range is Integer range 0 .. Max_Length;

-- Note that Max_Lines and Max_Length need to be static
type Paragraph_Body is array (Line_Range range <>, Length_Range range <>) of Character;

type Paragraph (Lines : Line_Range := 0; Line_Length : Length_Range := 0) is
   record
      Text : Paragraph_Body (1 .. Lines, 1 .. Line_Length);
   end record;

rationale

Determine the size and speed impact of unconstrained records having components depending on discriminants. Some compilers will allocate the maximum possible size to each object of the type; others will use pointers to the dependent components, incurring a possible heap performance penalty. Consider the possibility of using fixed-size components.