bcquality/microsoft/knowledge/performance/use-textbuilder-for-loop-string-assembly.md

bc-version	domain	keywords	technologies	countries	application-area
all	performance	textbuilder string-concatenation loop text allocation	al	w1	all

Use TextBuilder for loop-based string assembly

Description

Repeated Text := Text + ... concatenation inside a loop reallocates and copies the growing string on every iteration. In AL, TextBuilder is the platform type for constructing larger text payloads incrementally. StrSubstNo remains appropriate for formatting one message; TextBuilder is for many appends, especially inside loops.

Best Practice

Use TextBuilder.Append or AppendLine when assembling CSV rows, log payloads, JSON-ish diagnostic text, or other multi-line strings from repeated loop iterations. Convert to Text once, after the loop, with ToText().

See sample: use-textbuilder-for-loop-string-assembly.good.al.

Anti Pattern

Appending to the same Text variable on every iteration of a large loop. Each append copies the accumulated prefix again, so the cost grows with both row count and final string length.

See sample: use-textbuilder-for-loop-string-assembly.bad.al.