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Legacy

This page lists features of JLD2 that are kept for legacy purposes. In particular, the following sections describes the @load and @save macros. They have been the default for many users but they unnecessarily introduce new macro-based syntax. Over time a range of issues have been opened by new users struggling with them. Since their inception, the Julia language has improved significantly and macros may no longer be necessary in this case.

@save and @load macros

The @save and @load macros are the simplest way to interact with a JLD2 file. The @save macro writes one or more variables from the current scope to the JLD2 file. For example:

using JLD2
hello = "world"
foo = :bar
@save "example.jld2" hello foo

This writes the variables hello and foo to datasets in a new JLD2 file named example.jld2. The @load macro loads variables out of a JLD2 file:

@load "example.jld2" hello foo

This assigns the contents of the hello and foo datasets to variables of the same name in the current scope.

It is best practice to explicitly name the variables to be loaded and saved from a file, so that it is clear from whence these variables arise. However, for convenience, JLD2 also provides variants of @load and @save that do not require variables to be named explicitly. When called with no variable arguments, @save <filename> writes all variables in the global scope of the current module to file <filename>, while @load <filename> loads all variables in file <filename>. When called with no variable arguments, @load requires that the file name is provided as a string literal, i.e., it is not possible to select the file at runtime.

Additional customization is possible using assignment syntax and option passing:

@save "example.jld2" bye=hello bar=foo
@save "example.jld2" {compress=true} hello bar=foo
JLD2.@save — Macro
@save filename var1 [var2 ...]
@save filename {compress=true} var1 name2=var2

Write one or more variables var1,... from the current scope to a JLD2 file filename.

For interactive use you can save all variables in the current module's global scope using @save filename. More permanent code should prefer the explicit form to avoid saving unwanted variables.

Example

To save the string hello and array xs to the JLD2 file example.jld2:

hello = "world"
xs = [1,2,3]
@save "example.jld2" hello xs

For passing options to the saving command use {}

@save "example.jld2" {compress=true} hello xs

For saving variables under a different name use regular assignment syntax

@save "example.jld2" greeting=hello xarray = xs
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JLD2.@load — Macro
@load filename var1 [var2 ...]

Load one or more variables var1,... from JLD2 file filename into the current scope and return a vector of the loaded variable names.

For interactive use, the form @load "somefile.jld2" will load all variables from "somefile.jld2" into the current scope. This form only supports literal file names and should be avoided in more permanent code so that it's clear where the variables come from.

Example

To load the variables hello and foo from the file example.jld2, use

@load "example.jld2" hello foo
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