Basic/String-as-Boolean

Author: nightroman

Basic/String-as-Boolean/.test.ps1

@@ -0,0 +1,20 @@
+
+task Test-2.ps1 {
+	($1, $2, $3, $4, $5, $6 = .\Test-2.ps1)
+	equals $1 'Operator & works'
+	equals $2 'Dot-sourcing with | Out-Null works'
+	equals $3 'Dot-sourcing with > $null works'
+	equals $4 'value works as false'
+	equals $5 'cast1 is False'
+	assert ($6 -like 'Cannot convert value "System.String" to type "System.Boolean".*')
+}
+
+task Test-4.ps1 {
+	($1, $2, $3, $4, $5, $6 = .\Test-4.ps1)
+	equals $1 'Operator & works'
+	equals $2 'Dot-sourcing with | Out-Null works'
+	equals $3 'Dot-sourcing with > $null works'
+	equals $4 'value works as true'
+	equals $5 'cast1 is True'
+	assert ($6 -like 'Cannot convert value "System.String" to type "System.Boolean".*')
+}

Basic/String-as-Boolean/README.md

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+# String as Boolean
+
+The rule: empty strings are treated as false, not empty strings are treated as true (including strings "False").
+
+The rule works fine in Boolean expressions:
+
+```powershell
+if ($value) {...}
+if (!$value) {...}
+```
+
+The rule works fine in cast expressions:
+
+```powershell
+[bool]$value
+```
+
+But assigning a string to a typed variable of type `[bool]` may work or fail depending on invocation:
+
+```powershell
+[bool]$var = $value
+```
+
+**Scripts**
+
+- [Test-1.ps1](Test-1.ps1) shows how empty strings work as false
+- [Test-2.ps1](Test-2.ps1) calls `Test-1.ps1` and shows how assigning to `[bool]` may work or fail
+- [Test-3.ps1](Test-3.ps1) shows how not empty strings work as true
+- [Test-4.ps1](Test-4.ps1) calls `Test-3.ps1` and shows how assigning to `[bool]` may work or fail

Basic/String-as-Boolean/Test-1.ps1

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+
+# Empty strings work as false in Boolean expressions
+$value = ''
+if (!$value) {
+	'value works as false'
+}
+
+# Empty strings may be cast to [bool] as false
+$cast1 = [bool]$value
+"cast1 is $cast1"
+
+# But [bool]$var = '' may work or fail depending on invocation
+try {
+	[bool]$cast2 = $value
+	"cast2 is $cast2"
+}
+catch {
+	"$_"
+}

Basic/String-as-Boolean/Test-2.ps1

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+
+# Invocation by & works
+$null = & $PSScriptRoot\Test-1.ps1
+'Operator & works'
+
+# Dot-sourcing with | Out-Null works
+. $PSScriptRoot\Test-1.ps1 | Out-Null
+'Dot-sourcing with | Out-Null works'
+
+# Dot-sourcing with > $null works
+. $PSScriptRoot\Test-1.ps1 > $null
+'Dot-sourcing with > $null works'
+
+# But this dot-sourcing fails
+try {
+	. $PSScriptRoot\Test-1.ps1
+}
+catch {
+	"$_"
+}

Basic/String-as-Boolean/Test-3.ps1

@@ -0,0 +1,19 @@
+
+# Not empty strings work as true in Boolean expressions
+$value = 'False'
+if ($value) {
+	'value works as true'
+}
+
+# Not empty strings may be cast to [bool] as true
+$cast1 = [bool]$value
+"cast1 is $cast1"
+
+# But [bool]$var = ... may work or fail depending on invocation
+try {
+	[bool]$cast2 = $value
+	"cast2 is $cast2"
+}
+catch {
+	"$_"
+}

Basic/String-as-Boolean/Test-4.ps1

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+
+# Invocation by & works
+$null = & $PSScriptRoot\Test-3.ps1
+'Operator & works'
+
+# Dot-sourcing with | Out-Null works
+. $PSScriptRoot\Test-3.ps1 | Out-Null
+'Dot-sourcing with | Out-Null works'
+
+# Dot-sourcing with > $null works
+. $PSScriptRoot\Test-3.ps1 > $null
+'Dot-sourcing with > $null works'
+
+# But this dot-sourcing fails
+try {
+	. $PSScriptRoot\Test-3.ps1
+}
+catch {
+	"$_"
+}

README.md

@@ -62,6 +62,7 @@ to their directory. See also [TESTS]. Some scripts require
 - [Runspace pool memory leaks with `Close()`](Basic/RunspacePool)
 - [Statements are not expressions](Basic/Statements-are-not-expressions)
 - [ErrorRecord formatting may fail in the strict mode in the default host](Basic/Strict-mode-ErrorRecord-formatting)
+- [String as Boolean](Basic/String-as-Boolean)
 - [String constructor](Basic/String-constructor)
 - [String equality operators](Basic/String-equality-operators)
 - [`switch` is a looping construct](Basic/Switch-is-a-looping-construct)