Guard Pattern

[JohnnyUndercover]

I would like to add this pattern to the guidelines because it makes the code much more readable.
There is already something similar under the "Best Practices" topic called "if not then exit", but I don't think it is the same because it is only targeted at tables and therefore only for a specific guard.

Why use Guards?

The guard provides an early exit from a subroutine, and is a commonly used deviation from structured programming, removing one level of nesting and resulting in flatter code:[1] replacing if guard { ... } with if not guard: return; ....

Using guard clauses can be a refactoring technique to improve code. In general, less nesting is good, as it simplifies the code and reduces cognitive burden.
Guard (computer science) - Wikipedia

If you don't use guards, your code is likely to suffer from a large number of indentation and if-else relationships that prevent you from reading the code effortlessly from top to bottom. Because of the high number of intents and if-else statements, you have to jump through the code while keeping track of your current indentation level. This makes reading such a code mentally exhausting.

How does it look

Bad Code:

local procedure DoStuff() :Text
begin
   if SomeThingToCheck() then begin
      // Logic with a lot of code here
     exit(SomeResult);
   end else
      exit(AnotherResult);
   end;
end;

Good Code:

local procedure DoStuff() :Text
begin
   if not SomeThingToCheck() then
      exit(AnotherResult);
   
   // Logic with a lot of code here
   exit(SomeResult);
end;

Example 1

Bad Code

internal procedure GetBankFileName(BankAccount: Record "Bank Account"): Text[250]
begin
    if (BankAccount."AMC Bank File Name" <> '') then begin
        if (StrPos(BankAccount."AMC Bank File Name", '%1') <> 0) then
            exit(StrSubstNo(BankAccount."AMC Bank File Name", Format(CreateDateTime(Today(), Time()), 0, '<Year4><Month,2><Day,2>_<Hours24,2><Minutes,2><Second,2>')))
        else
            exit(BankAccount."AMC Bank File Name");
    end else
        exit(BankAccount."AMC Bank Name" + FileExtTxt);
end;

internal procedure GetBankFileName(BankAccount: Record "Bank Account"): Text[250]
begin
    if BankAccount."AMC Bank File Name" = '' then
        exit(BankAccount."AMC Bank Name" + FileExtTxt);

    if StrPos(BankAccount."AMC Bank File Name", '%1') = 0 then
        exit(BankAccount."AMC Bank File Name");

    exit(StrSubstNo(BankAccount."AMC Bank File Name", Format(CreateDateTime(Today(), Time()), 0, '<Year4><Month,2><Day,2>_<Hours24,2><Minutes,2><Second,2>')));
end;

Example 2

Bad Code

procedure DefineCoupling(RecordID: RecordID; var CRMID: Guid; var CreateNew: Boolean; var Synchronize: Boolean; var Direction: Option): Boolean
var
    CRMIntegrationRecord: Record "CRM Integration Record";
    CouplingRecordBuffer: Record "Coupling Record Buffer";
    CRMCouplingRecord: Page "CRM Coupling Record";
begin
    AssertTableIsMapped(RecordID.TableNo);
    CRMCouplingRecord.SetSourceRecordID(RecordID);
    if CRMCouplingRecord.RunModal() = ACTION::OK then begin
        CRMCouplingRecord.GetRecord(CouplingRecordBuffer);
        if CouplingRecordBuffer."Create New" then
            CreateNew := true
        else
            if not IsNullGuid(CouplingRecordBuffer."CRM ID") then begin
                CRMID := CouplingRecordBuffer."CRM ID";
                CRMIntegrationRecord.CoupleRecordIdToCRMID(RecordID, CouplingRecordBuffer."CRM ID");
                if CouplingRecordBuffer.GetPerformInitialSynchronization() then begin
                    Synchronize := true;
                    Direction := CouplingRecordBuffer.GetInitialSynchronizationDirection();
                end;
            end else
                exit(false);
        exit(true);
    end;
    exit(false);
end;

Good Code

procedure DefineCoupling(RecordID: RecordID; var CRMID: Guid; var CreateNew: Boolean; var Synchronize: Boolean; var Direction: Option): Boolean
var
    CRMIntegrationRecord: Record "CRM Integration Record";
    CouplingRecordBuffer: Record "Coupling Record Buffer";
    CRMCouplingRecord: Page "CRM Coupling Record";
begin
    AssertTableIsMapped(RecordID.TableNo);
    CRMCouplingRecord.SetSourceRecordID(RecordID);
    if CRMCouplingRecord.RunModal() <> ACTION::OK then
        exit(false);
        
    CRMCouplingRecord.GetRecord(CouplingRecordBuffer);
    if CouplingRecordBuffer."Create New" then begin
        CreateNew := true
        exit(true);
    end;

    if IsNullGuid(CouplingRecordBuffer."CRM ID") then
        exit(false);

    CRMID := CouplingRecordBuffer."CRM ID";
    CRMIntegrationRecord.CoupleRecordIdToCRMID(RecordID, CouplingRecordBuffer."CRM ID");
    if CouplingRecordBuffer.GetPerformInitialSynchronization() then begin
        Synchronize := true;
        Direction := CouplingRecordBuffer.GetInitialSynchronizationDirection();
    end;
    exit(true);
end;

[pri-kise]

I really like this pattern.