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BSL257 — Unary Plus sign in string concatenation

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Summary

Unary Plus sign in string concatenation

Identifiers

Field Value
Rule code BSL257
Compatible alias UnaryPlusInConcatenation
Severity ERROR
Enabled by default Yes
Implemented Yes
Tags suspicious, brainoverload

Behavior

  • The public identifier BSL257 and alias UnaryPlusInConcatenation are stable.
  • The rule reports the cases documented on this page.
  • Suppressions and project configuration are applied before publication.
  • The rule requires neither an external analyzer nor network access.

Configuration and suppression

BSL### is the primary stable identifier. The compatible alias is accepted in select, ignore, and compatible block suppression comments.

[tool.onec-hbk-bsl]
select = ["BSL257"]
ignore = ["UnaryPlusInConcatenation"]

All three suppression families support both a current line and a range. When an opening comment follows code, it affects only that line. Use any one form:

  • noqa:
Value = "example";  // noqa: BSL257
  • bsl-disable:
Value = "example";  // bsl-disable: BSL257
  • compatible BSLLS form:
Value = "example";  // BSLLS:UnaryPlusInConcatenation-off

When the same opening comment is on a line by itself, it starts a range. Close it with the matching marker from the same family:

// noqa: BSL257
// code without this diagnostic
// noqa-enable: BSL257

// bsl-disable: BSL257
// code without this diagnostic
// bsl-enable: BSL257

// BSLLS:UnaryPlusInConcatenation-off
// code without this diagnostic
// BSLLS:UnaryPlusInConcatenation-on

To disable the rule until the end of the file, omit the closing noqa-enable, bsl-enable, or BSLLS:…-on marker.

Opening and closing markers must belong to the same family.

Description

When concatenating strings, a developer may mistakenly write code String + + String2, i.e. the second plus, the platform recognizes as unary and tries to cast to a number, which in most cases will lead to a runtime exception