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Function Repository Resource:

InheritedBlock

Source Notebook

Similar to Block, except values of local symbols are not cleared when entering the block

Contributed by: Richard Hennigan (Wolfram Research)

ResourceFunction["InheritedBlock"][{x,y,},expr]

specifies that expr is to be evaluated with changes to the symbols x,y, localized to the block.

ResourceFunction["InheritedBlock"][{x=x0,},expr]

defines initial local values for x,.

Details and Options

ResourceFunction["InheritedBlock"] allows you to set up an environment in which the values of variables can temporarily be changed while keeping their initial values intact.
ResourceFunction["InheritedBlock"] is like Block, but values assigned to x, y, are not cleared when entering the block.
When the execution of the block is finished, the original values of these symbols are restored.
ResourceFunction["InheritedBlock"] affects only the values of symbols, not their names.
ResourceFunction["InheritedBlock"] has attribute HoldAll.
ResourceFunction["InheritedBlock"] implements dynamic scoping of variables.

Examples

Basic Examples

Make temporary changes to the value of a symbol:

In[1]:=
x = 1;
ResourceFunction["InheritedBlock"][{x}, x = 2; x]
Out[2]=

The original value is restored:

In[3]:=
x
Out[3]=

Temporarily modify definitions of a function:

In[4]:=
f[x_] := x + 1;
ResourceFunction["InheritedBlock"][{f}, f[5] = "No!"; f /@ Range[10]]
Out[5]=

The changes to the definition of f only persisted within the block:

In[6]:=
f /@ Range[10]
Out[6]=

Make temporary changes to multiple symbols:

In[7]:=
{x, y} = {1, 2};
ResourceFunction["InheritedBlock"][{x, y}, {x, y} = {3, 4}; x + y]
Out[8]=

Both symbols are restored:

In[9]:=
{x, y}
Out[9]=

Scope

Modify Protected functions for one evaluation:

In[10]:=
ResourceFunction["InheritedBlock"][{Reverse},
 Unprotect[Reverse];
 HoldPattern[Reverse[xyz]] = zyx;
 Reverse /@ {{1, 2, 3}, xyz, {a, b, c}}
 ]
Out[10]=

The normal behavior is unchanged:

In[11]:=
Reverse /@ {{1, 2, 3}, xyz, {a, b, c}}
Out[11]=

The Attributes are restored as well:

In[12]:=
Attributes[Reverse]
Out[12]=

Temporarily change the default formatting of expressions:

In[13]:=
ResourceFunction["InheritedBlock"][{Graphics},
 Unprotect[Graphics]; FormatValues[Graphics] =.;
 MakeBoxes[Graphics[a_, b___], StandardForm] := RowBox[{"Graphics", "[", MakeBoxes[a, StandardForm], ",", ToBoxes[Iconize[Sequence[b], "Options"]], "]"}];
 Table[Echo[
   Graphics[{RandomColor[], Disk[]}, ImageSize -> 25, Background -> RandomColor[]]], 3]
 ]
Out[13]=

Applications

Have cloud deployments that would otherwise be deployed to anonymous cloud objects go to a specific target:

In[14]:=
ResourceFunction["InheritedBlock"][{CloudObject},
 Unprotect[CloudObject];
 CloudObject[] = CloudObject["temp"];
 CloudDeploy[APIFunction[{}, DateList[] &]]
 ]
Out[14]=

The normal behavior is unchanged:

In[15]:=
CloudDeploy[APIFunction[{}, DateList[] &]]
Out[15]=

Properties and Relations

InheritedBlock localizes values only; it does not create new symbols:

In[16]:=
x = 1;
ResourceFunction["InheritedBlock"][{x}, x =.; Print[x]]
In[17]:=
x
Out[17]=

Module creates new symbols:

In[18]:=
Module[{x}, Print[x]]

Possible Issues

Using Condition in InheritedBlock does not work the same way as Block, Module and With:

In[19]:=
g[1] := Block[{x = Echo[1]}, x /; False];
g[2] := Module[{x = Echo[2]}, x /; False];
g[3] := With[{x = Echo[3]}, x /; False];
g[4] := ResourceFunction["InheritedBlock"][{x = Echo[4]}, x /; False];
g /@ Range[4]
Out[20]=

The behavior is also different for held replacements:

In[21]:=
Hold[1, 2, 3] /. n_Integer :> Block[{x = n + 1}, x /; True]
Out[21]=
In[22]:=
Hold[1, 2, 3] /. n_Integer :> Module[{x = n + 1}, x /; True]
Out[22]=
In[23]:=
Hold[1, 2, 3] /. n_Integer :> With[{x = n + 1}, x /; True]
Out[23]=
In[24]:=
Hold[1, 2, 3] /. n_Integer :> ResourceFunction["InheritedBlock"][{x = n + 1}, x /; True]
Out[24]=

Symbols cleared with ClearAll within an InheritedBlock will not be restored:

In[25]:=
x = 1;
ResourceFunction["InheritedBlock"][{x}, ClearAll[x]];
x
Out[23]=

Compare to Block, which protects its symbols from ClearAll:

In[26]:=
x = 1;
Block[{x}, ClearAll[x]];
x
Out[27]=

Clear is safe to use:

In[28]:=
x = 1;
ResourceFunction["InheritedBlock"][{x}, Clear[x]];
x
Out[29]=

Requirements

Wolfram Language 11.3 (March 2018) or above

Resource History

See Also

License Information