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README.md

Ada Type Ranges

Demonstrates Ada's strong type system with range constraints - compile-time and runtime safety for numeric values with explicit valid ranges.

The Problem

In most programming languages, numeric types accept any value within their storage capacity:

int age = 200;        // Compiles fine, but humans don't live to 200
int floor = -100;     // Compiles fine, but buildings don't have 100 basement levels
int httpStatus = 999; // Compiles fine, but not a valid HTTP status

These invalid values slip through and cause bugs that only manifest at runtime - or worse, silently corrupt data.

The Solution

Ada allows defining types with explicit value ranges:

type Age_Type is range 0 .. 150;
type Floor_Type is range -5 .. 100;
type HTTP_Status is range 100 .. 599;

Key Benefits

Compile-Time: Exhaustive Case Statements

Case statements must cover ALL possible values. Missing cases result in a compile error:

type Age_Type is range 0 .. 150;

case Age is
   when 0 .. 17 => Put_Line("Minor");
   when 18 .. 64 => Put_Line("Adult");
   -- COMPILE ERROR: missing case value(s) 65 .. 150
end case;

Runtime: Constraint Violations

Assigning out-of-range values raises Constraint_Error:

Age : Age_Type := 200;  -- Raises Constraint_Error at runtime

Subtypes: Named Subranges

Define meaningful subranges for cleaner code:

type HTTP_Status is range 100 .. 599;
subtype Success is HTTP_Status range 200 .. 299;
subtype Client_Error is HTTP_Status range 400 .. 499;
subtype Server_Error is HTTP_Status range 500 .. 599;

Files

File Description
type_ranges_demo.adb Main demo showing Age, Floor, and HTTP Status examples
incomplete_case_demo.adb Intentionally fails to compile - demonstrates exhaustiveness checking

How to Run

Using Docker (Recommended)

# Build the image
docker build -t ada-type-ranges .

# Run all demos
docker run --rm ada-type-ranges

# Run only the main demo
docker run --rm ada-type-ranges sh -c "gnatmake -q type_ranges_demo.adb && ./type_ranges_demo"

# See the compile error demo
docker run --rm ada-type-ranges gnatmake incomplete_case_demo.adb

Local Installation

Requires GNAT (GNU Ada Compiler):

# Debian/Ubuntu
apt-get install gnat

# macOS with Homebrew
brew install gnat

# Compile and run
gnatmake type_ranges_demo.adb
./type_ranges_demo

# See the compile error
gnatmake incomplete_case_demo.adb

Expected Output

Main Demo

=== Domain 1: Age (0..150) ===
Age 0:   Newborn
Age 2:   Toddler
Age 10:  Child
Age 16:  Teenager
Age 35:  Adult
Age 75:  Senior

=== Domain 2: Building Floors (-5..100) ===
Floor -3: Underground Parking Level -3
Floor 0:  Ground Floor / Lobby
Floor 5:  Lower Floors (Commercial)
Floor 50: Residential Floors
Floor 95: Penthouse Level

=== Domain 3: HTTP Status Codes (100..599) ===
Status 200: 2xx Success
Status 404: 4xx Client Error
Status 500: 5xx Server Error

=== Runtime Constraint Violation ===
Attempting to assign 200 to Age_Type (range 0..150)...
CAUGHT: Constraint_Error!
   Ada prevented an invalid value at runtime.

Compile Error Demo

incomplete_case_demo.adb:10:07: error: missing case value(s) 65 .. 150
gnatmake: "incomplete_case_demo.adb" compilation error
The compiler caught the missing case at compile time!

References